JOSÉ A. CABRANES, Circuit Judge:

The question presented is whether plaintiff Disability Advocates, Inc. ("DAI")—a private nonprofit organization contracted to provide services to New York State's protection and advocacy ("P & A") system under the Protection and Advocacy for Individuals with Mental Illness Act ("PAIMI"), 42 U.S.C. § 10801 et seq.—has standing to sue various state agencies and officials on behalf of certain individuals with mental illness residing in New York City for an alleged violation of the "integration mandate" of Title II of the Americans with Disabilities Act ("ADA"), 42 U.S.C. § 12132, and Section 504 of the Rehabilitation Act, 29 U.S.C. § 794.

We conclude that because DAI does not have the "indicia of membership" required of nonmembership organizations for "associational standing," see Hunt v. Wash. State Apple Adver. Comm'n, 432 U.S. 333, 343, 97 S.Ct. 2434, 53 L.Ed.2d 383 (1977), DAI fails to satisfy the standing requirements under Article III of the United States Constitution as interpreted by the Supreme Court.

Because DAI lacks standing, we must also decide whether the intervention of the United States—which occurred after the determination of liability by the United States District Court for the Eastern District of New York (Nicholas G. Garaufis, Judge) but before the imposition of a remedy—was sufficient to cure the jurisdictional defect that would have barred the District Court from hearing the suit as originally brought. We hold that in the circumstances presented here it was not sufficient. We therefore vacate the March 1, 2010 judgment and remedial order of the District Court and dismiss the action for want of jurisdiction.

BACKGROUND

A. The PAIMI

In 1986, Congress enacted PAIMI1 in order to "ensure that the rights of individuals with mental illness are protected" and to "assist States to establish and operate a protection and advocacy system for individuals with mental illness which will ... protect and advocate the rights of such individuals through activities to ensure the enforcement of the Constitution and Federal and State statutes." 42 U.S.C. § 10801(b)(1), (b)(2)(A).2 In line with these objectives, PAIMI conditions certain federal funding for states on the establishment of protection and advocacy ("P & A") systems. 42 U.S.C. § 10803(2)(A). The designated P & A system may be either an independent state agency or a private entity. 42 U.S.C. § 15044(a), incorporated by reference in 42 U.S.C. § 10802(2). In turn, P & A systems are authorized to "pursue administrative, legal, and other appropriate remedies to ensure the protection of individuals with mental illness who are receiving care or treatment in the State." 42 U.S.C. § 10805(a)(1)(B).

New York has designated the Commission on Quality of Care and Advocacy for Persons with Disabilities ("CQCAPD") as the State's P & A system for persons with mental illness pursuant to PAIMI, 42 U.S.C. § 10821.3 See N.Y. Mental Hyg. Law § 45.07(p)4; 42 U.S.C. § 10821. In 1989, CQCAPD entered into a contract with DAI as permitted by 42 U.S.C. § 108045 and New York Mental Hygiene Law § 45.07(i).6 See Disability Advocates, Inc. v. Pataki, No. 03-cv-3209 (NGG), Zucker Aff. ¶ 6, Docket No. 205 (E.D.N.Y. Dec. 3, 2007) ("Zucker Aff.").7 That contract "designates DAI as an authorized PAIMI agency and ... authorizes DAI to provide protection and advocacy services to individuals with mental illness throughout the state." Id.

B. Procedural History

On July 1, 2003, DAI initiated this action by filing suit against the Governor of the State of New York, the New York State Department of Health, the New York State Department of Mental Health, and the commissioners of those two agencies (collectively, the "State" or "defendants")8 on behalf of its "constituents": individuals with mental illness as defined under 42 U.S.C. § 10802(4), who reside, or might one day reside, in specified "adult homes" in New York City.9 Compl. ¶ 9. DAI alleged that the mental health system run by the State violated the "integration mandate" of Title II of the ADA, 42 U.S.C. § 12132, and Section 504 of the Rehabilitation Act, 29 U.S.C. § 794, which requires the provision of mental health services "in the most integrated setting appropriate to the needs of qualified individuals with disabilities." 28 CFR § 35.130(d); see Olmstead v. L.C. ex rel. Zimring, 527 U.S. 581, 607, 119 S.Ct. 2176, 144 L.Ed.2d 540 (1999) (holding that the provision of mental health services in an institutionalized setting when the recipients are capable and willing to live in a manner more fully integrated into the community constitutes a violation of Title II of the ADA, provided that such integration can be reasonably accommodated). DAI sought declaratory and injunctive relief that would require the State to "shift[ ] residents and funds [away] from impacted [sic] adult homes to community-based residential programs" and to end "[t]he State's practice of knowingly placing and maintaining individuals with serious mental illness in impacted [sic] adult homes." Compl. ¶¶ 118, 165.

After discovery, the State brought a motion for summary judgment challenging, among other things, DAI's standing to sue on behalf of its constituents under PAIMI and Article III of the United States Constitution. The District Court denied the motion for summary judgment and rejected the standing argument, concluding that DAI had statutory standing pursuant to § 10805(a)(1)(B)10 and satisfied the minimum requirements of constitutional standing under Article III. Disability Advocates, Inc. v. Paterson, 598 F.Supp.2d 289, 307-10 (E.D.N.Y.2009) ("DAI I"). The case then proceeded to trial.

Following a five-week bench trial, the District Court concluded that "[i]n carrying out their administration of New York's mental health service system, [d]efendants have denied thousands of individuals with mental illness in New York City the opportunity to receive services in the most integrated setting appropriate to their needs." Disability Advocates, Inc. v. Paterson, 653 F.Supp.2d 184, 314 (E.D.N.Y.2009) ("DAI II"). Accordingly, in a September 8, 2009 memorandum setting forth findings of fact and conclusions of law, the District Court determined that DAI had adequately "proven that [d]efendants discriminated against DAI's constituents in violation of the integration mandate of the Americans with Disabilities Act and the Rehabilitation Act." Id. The Court announced its intention to enter "the appropriate injunctive remedy" following further briefing. Id.

On October 23, 2009, more than six years after the complaint was filed, the United States moved to intervene at the remedial stage of the litigation pursuant to Rule 24 of the Federal Rules of Civil Procedure.11 United States Motion to Intervene, Docket No. 358 (E.D.N.Y. Oct. 23, 2009). Noting that "the United States' [m]otion comes very late in the litigation process," the District Court nevertheless determined that intervention would not "prejudice the original parties or unduly delay the proceedings concerning the appropriate injunctive remedy to be imposed." Disability Advocates, Inc. v. Paterson, No. 03-cv-3209, 2009 WL 4506301, at *2 (E.D.N.Y. Nov. 23, 2009). Accordingly, the Court granted the United States' motion. Id. at *4.12

On March 1, 2010, the District Court rejected the State's proposed remedial plan as "unreasonable and inadequate," Disability Advocates, Inc. v. Paterson, No. 03-cv-3209, 2010 WL 786657, at *7 (E.D.N.Y. Mar. 1, 2010), and entered a judgment and remedial order adopting DAI's proposed remedy with minor modifications, see Judgment and Remedial Order, Docket No. 405 (E.D.N.Y. Mar. 1, 2010). Among other things, the remedy fashioned by the District Court required the State to ensure that, within four years of the entry of the District Court's order,

Id. at 3 (emphasis supplied).13 Over the objection of defendants, the District Court ordered that a court-appointed monitor oversee the State's compliance with the injunctive relief imposed by the District Court. Id. at 8-9. By Order dated February 23, 2011, this Court granted a stay of the remedial order pending the outcome of this appeal.

C. This Appeal

Defendants appeal from the March 1, 2010 judgment and remedial order of the District Court. On appeal, they argue, among other things, that the District Court erred in concluding that DAI had constitutional standing to pursue this litigation. State's Br. 74-79. Because standing is "the threshold question in every federal case" and raises an issue with respect to the Court's subject-matter jurisdiction, we turn first to that claim. Denney v. Deutsche Bank AG, 443 F.3d 253, 263 (2d Cir.2006) (quoting Warth v. Seldin, 422 U.S. 490, 498, 95 S.Ct. 2197, 45 L.Ed.2d 343 (1975)).14 And because we conclude that DAI lacked standing and that the intervention of the United States was insufficient to cure that jurisdictional defect, we dismiss the action for want of jurisdiction.

DISCUSSION

A. Standard of Review

Whether a plaintiff has standing to sue is a question of law, which we review de novo. See, e.g., Carver v. City of New York, 621 F.3d 221, 225 (2d Cir.2010).

B. Associational Standing

What constitutes the "irreducible constitutional minimum of standing" is firmly established. Lujan v. Defenders of Wildlife, 504 U.S. 555, 560, 112 S.Ct. 2130, 119 L.Ed.2d 351 (1992). The limitation on the federal judicial power under the United States Constitution to "cases" and "controversies," U.S. Const. art. III, § 2, requires that the party invoking federal jurisdiction demonstrate "(1) injury-in-fact, which is a `concrete and particularized' harm to a `legally protected interest'; (2) causation in the form of a `fairly traceable' connection between the asserted injury-in-fact and the alleged actions of the defendant; and (3) redressability, or a non-speculative likelihood that the injury can be remedied by the requested relief." W.R. Huff Asset Mgmt. Co. v. Deloitte & Touche LLP, 549 F.3d 100, 106-07 (2d Cir.2008) (quoting Lujan, 504 U.S. at 560-61, 112 S.Ct. 2130).

When an association asserts standing solely as the representative of its members, it "must allege that its members, or any one of them, are suffering immediate or threatened injury as a result of the challenged action of the sort that would make out a justiciable case had the members themselves brought suit." Warth v. Seldin, 422 U.S. 490, 511, 95 S.Ct. 2197, 45 L.Ed.2d 343 (1975). This requirement was further elaborated in Hunt v. Wash. State Apple Adver. Comm'n, 432 U.S. 333, 97 S.Ct. 2434, 53 L.Ed.2d 383 (1977), in which the Supreme Court announced the current three-pronged test for "associational standing." Under Hunt,

432 U.S. at 343, 97 S.Ct. 2434. Two decades after Hunt, the Supreme Court clarified that the first two of these requirements are constitutional limitations, whereas the third requirement is a "prudential limitation" that may be abrogated by Congress. United Food & Commercial Workers Union Local 751 v. Brown Grp., 517 U.S. 544, 557, 116 S.Ct. 1529, 134 L.Ed.2d 758 (1996).

The Hunt Court concluded that the Washington State Apple Advertising Commission—a state agency charged by statute with the promotion and protection of the State's apple industry on behalf of apple growers and dealers—was not a membership organization, but it nevertheless satisfied the first prong of the associational standing test because "in a very real sense ... the Commission represent[ed] the State's growers and dealers and provide[d] the means by which they express[ed] their collective views and protect[ed] their collective interests." Id. at 344-45, 97 S.Ct. 2434. Furthermore, the apple growers and dealers "alone elect[ed] the members of the Commission; they alone [could] serve on the Commission; they alone finance[d] its activities, including the costs of [litigating Hunt], through assessments levied upon them." Id.

In sum, the Supreme Court reasoned that, although the Commission did not have "members" in the "traditional" sense, its "constituency" possessed "all the indicia of membership." Id. We have therefore recognized that—assuming the other criteria for associational standing are met— non-membership organizations may sue in a representative capacity when they "function[ ] effectively as a membership organization." In re Holocaust Victim Assets Litig., 225 F.3d 191, 196 (2d Cir.2000).

On the threshold jurisdictional question of standing, the only dispute is whether DAI—which is not a membership organization—satisfies the first prong of the test for associational standing under Hunt. Defendants argue that DAI cannot meet this requirement (i.e. that its members would otherwise have standing to sue in their own right) because DAI's constituents lack two key indicia of membership: representation and control. In turn, DAI and the United States contend that Hunt does not render representation and control the only indicia of membership sufficient to create "members" out of "constituents" for purposes of associational standing.

Pursuant to PAIMI, P & A systems must ensure that they are responsive to the needs of the community they were created to represent. Accordingly, the governing board of all P & A systems must be "composed of ... members ... who broadly represent or are knowledgeable about the needs of the clients served by the system"; such members are defined to include "individuals who have received or are receiving mental health services and family members of such individuals." 42 U.S.C. § 10805(c)(1)(B). In addition, a P & A system must:

Id. § 10805(a)(6)(B-C). Finally, PAIMI also requires that P & A systems establish a grievance procedure for clients or prospective clients to "assure that individuals with mental illness have full access to the services of the system." Id. § 10805(a)(9).

Whether these protections are sufficient to connote the "indicia of membership" required for associational standing under Hunt has not heretofore been addressed in this Circuit. Some, but not all, courts of appeals to address the question have concluded that they are sufficient. See Or. Advocacy Ctr. v. Mink, 322 F.3d 1101, 1110 (9th Cir.2003) (concluding that the "constituents" of Oregon's P & A system "possess many indicia of membership— enough to satisfy the purposes that undergird the concept of associational standing: that the organization is sufficiently identified with and subject to the influence of those it seeks to represent as to have a `personal stake in the outcome of the controversy.'" (quoting Vil. of Arlington Heights v. Metro. Hous. Dev. Corp., 429 U.S. 252, 261, 97 S.Ct. 555, 50 L.Ed.2d 450 (1977))); Doe v. Stincer, 175 F.3d 879, 886 (11th Cir.1999) (concluding that the requirements under § 10805 ensure that "[m]uch like members of a traditional association, the constituents of the [P & A system] possess the means to influence the priorities and activities the [system] undertakes"); but see Ass'n for Retarded Citizens of Dall. v. Dall. Cnty. Mental Health & Mental Retardation Ctr. Bd. of Trs., 19 F.3d 241, 244 (5th Cir.1994) (concluding that Texas's P & A system bore "no relationship to [a] traditional membership group[ ], because most of its `clients' . . . are unable to participate in and guide the organization's efforts"); Mo. Prot. & Advocacy Servs., Inc. v. Carnahan, 499 F.3d 803, 810 (8th Cir.2007) (concluding same with respect to Missouri's P & A system).

We need not—and do not—decide which of our sister circuits has the better of this argument, because DAI is not a P & A system but a contractor to the system, see notes 5-6, ante, designated to provide protection and advocacy services under PAIMI. Zucker Aff. ¶ 6. This distinction is critical to the question of whether DAI has associational standing because the sole basis cited in both Stincer (Eleventh Circuit) and Mink (Ninth Circuit) for finding that P & A systems have associational standing to sue on behalf of individuals with mental illness is that § 10805 affords individuals with mental illness (and their families and representatives) the requisite "indicia of membership" in the administration of the system.

The District Court did not consider whether DAI is subject to any of the statutory requirements under § 10805 such that it might satisfy the constitutional requirements for standing under Hunt. More importantly, however, DAI does not claim that its constituents have a sufficiently active affiliation with the organization. Cf. Hunt, 432 U.S. at 344-45, 97 S.Ct. 2434 (recognizing that the apple growers and dealers "alone elect the members of the Commission; they alone may serve on the Commission; [and] they alone finance its activities"). Tellingly, there is scant evidence in the record that the individuals with mental illness whom DAI purports to represent have the power to elect its directors, make budget decisions, or influence DAI's activities or litigation strategies. For instance, the record does not contain the contract between CQCAPD and DAI. Nor does it contain agendas, minutes, or other evidence regarding the quarterly meetings between DAI and CQCAPD's Advisory Council; names and descriptions of the members of the Advisory Council; or ways that individuals with mental illness convey information, requests, or inquiries to the Advisory Council. Finally, the record does not establish that DAI ever notified its "constituents" or any of their legal guardians that it was filing this suit purportedly on their behalf. Accordingly, DAI has failed to satisfy its burden of establishing the elements of its purported associational standing. Lujan, 504 U.S. at 561, 112 S.Ct. 2130.

To the extent DAI relies on District Court cases in this Circuit for the proposition that contractors have associational standing to sue on behalf of individuals with mental illness, those cases are inapposite in one of two ways. First, cases that have recognized the associational standing of non-membership organizations have almost exclusively concerned P & A systems rather than P & A contractors such as DAI. See, e.g., State of Conn. Office of Prot. & Advocacy for Persons with Disabilities v. Connecticut, 706 F.Supp.2d 266, 281-83 (D.Conn.2010). Second, those cases that have recognized the distinction between systems and contractors of systems have elided the constitutional dimensions of associational standing entirely. See, e.g., Rubenstein v. Benedictine Hosp., 790 F.Supp. 396 (N.D.N.Y.1992). They are therefore of little value to DAI and the United States in this case, which turns entirely on whether DAI meets the constitutional threshold for associational standing set forth by the Supreme Court.

Hunt held that the Constitution requires that the constituents of a non-membership organization manifest the "indicia of membership" for that organization to have associational standing to sue on their behalf. On the record before us, DAI has established that CQCAPD, New York's P & A system, is bound by the statutory requirements of § 10805, but we can find no support for the proposition that DAI itself is subject to those requirements or has adopted the same statutory protections. Without those protections, there is no evidence that the individuals with mental illness on behalf of whom DAI brought this case have anything approaching the indicia of membership that is required under Hunt, much less that DAI "function[s] effectively as a membership organization." See In re Holocaust Litig., 225 F.3d at 196. We therefore hold that DAI has failed to satisfy the constitutional requirements for associational standing prescribed by the Supreme Court in Hunt and its progeny.15

C. Intervention

The United States argues that even if DAI lacks standing to pursue this claim, the intervention of the United States after the completion of the liability phase of the case is sufficient to permit the case to move forward. See United States Br. 77-80. We disagree.

We have long recognized that "`if jurisdiction is lacking at the commencement of [a] suit, it cannot be aided by the intervention of a [plaintiff] with a sufficient claim.'" Pressroom Unions-Printers League Income Sec. Fund v. Cont'l Assurance Co., 700 F.2d 889, 893 (2d Cir.1983) (quoting Pianta v. H.M. Reich Co., 77 F.2d 888, 890 (2d Cir.1935)) (brackets in original); see also 7C C. Wright, A. Miller, & M. Kane, Federal Practice and Procedure § 1917, at 457 (3d ed. 2005) ("Intervention cannot cure any jurisdictional defect that would have barred the federal court from hearing the original action."). This is no casual observation; our recognition that "[t]he right to intervene presupposes an action duly brought," Pianta, 77 F.2d at 890, reflects the Supreme Court's long-held understanding that where a "cause of action ha[s] not accrued to the [party] who undertook to bring the suit originally.... intervention [can]not cure th[e] vice in the original suit." U.S. ex rel. Tex. Portland Cement Co. v. McCord, 233 U.S. 157, 163-64, 34 S.Ct. 550, 58 L.Ed. 893 (1911); accord Town of West Hartford v. Operation Rescue, 915 F.2d 92, 95 (2d Cir.1990) ("[I]t is fundamental that an intervening claim cannot confer subject matter jurisdiction over the action it seeks to join.").

The logic that underlies this rule is clear enough. Intervention is a procedural means for entering an existing federal action. See Canatella v. California, 404 F.3d 1106, 1113 (9th Cir.2005). The Federal Rules of Civil Procedure "do not extend or limit the jurisdiction of the district courts." Fed R. Civ. P. 82. That is, Rule 24 does not itself provide a basis for jurisdiction. Accordingly, "since intervention contemplates an existing suit in a court of competent jurisdiction and because intervention is ancillary to the main cause of action, intervention will not be permitted to breathe life into a `nonexistent' law suit." Fuller v. Volk, 351 F.2d 323, 328 (3d Cir.1965). Indeed, this rule is so deeply entrenched in our jurisprudence that it is an axiomatic principle of federal jurisdiction in every circuit to have addressed the question. See, e.g., Hofheimer v. McIntee, 179 F.2d 789, 792 (7th Cir.1950) ("An existing suit within the court's jurisdiction is a prerequisite of an intervention, which is an ancillary proceeding in an already instituted suit.") (quotation marks omitted); see also Canatella, 404 F.3d at 1113 ("Because Rule 24 cannot extend federal jurisdiction[,]. . . intervention as of right cannot be used to circumvent Younger [v. Harris, 401 U.S. 37, 91 S.Ct. 746, 27 L.Ed.2d 669 (1971)] abstention."); Black v. Cent. Motor Lines, Inc., 500 F.2d 407, 408 (4th Cir.1974) ("By its very nature intervention presupposes pendency of an action in a court of competent jurisdiction."); Kendrick v. Kendrick, 16 F.2d 744, 745 (5th Cir.1926) (explaining that an existing lawsuit within the court's jurisdiction is a prerequisite of intervention); Brictson Mfg. Co. v. Woodrough, 284 F. 484, 487 (8th Cir.1922) (same).

In Hackner v. Guar. Trust Co., 117 F.2d 95 (2d Cir.1941), we recognized a district court's discretion to treat the pleading of an intervenor as a separate action in order to adjudicate the claims raised by the intervenor even if the underlying claim was jurisdictionally deficient. There, plaintiffs sought to amend the complaint by substituting one party for two others twenty two days after the complaint was filed and before any action by the defendants had been taken. Rather than start again, we distinguished Pianta and its progeny and permitted the suit to proceed because the intervention had occurred before any action by the defendants had been taken. Id. at 99. As Judge Charles E. Clark, the chief architect of the Federal Rules of Civil Procedure, noted, "whether the matter is treated as one of amendment . . . or of commencement of a new action," the action can continue "without the delay and expense of a new suit, which at long last will merely bring the parties to the point where they now are." Id. Since Hackner, this prudential approach has found favor in other courts. See, e.g., Miller & Miller Auctioneers, Inc. v. G.W. Murphy Indus., Inc., 472 F.2d 893, 895 (10th Cir.1973).

Unlike in Hackner, however, the United States intervened in this case after the trial had concluded. Permitting this case to continue would allow the Hackner exception (that curative interventions be construed as separate actions when they are effected at the beginning of the proceedings) to swallow the clearly-established constitutional rule that intervention cannot cure any jurisdictional defect that would have barred the federal court from hearing the original action.

The fact that the United States adopted in its complaint the findings of fact and conclusions of law of the District Court does not justify the conclusion that we should exercise our discretion to permit this case to proceed. The relevant question under Hackner is not whether the curative intervenor is prepared to take the case "as he finds it" for the sake of judicial economy, but rather, whether he entered sufficiently early in the litigation to ensure that parties "invok[ing] the court's jurisdiction have `alleged such a personal stake in the outcome of the controversy as to assure that concrete adverseness which sharpens the presentation of issues upon which the court so largely depends for illumination of difficult . . . questions.'" Duke Power Co. v. Carolina Envtl. Study Grp., 438 U.S. 59, 72, 98 S.Ct. 2620, 57 L.Ed.2d 595 (1978) (quoting Baker v. Carr, 369 U.S. 186, 204, 82 S.Ct. 691, 7 L.Ed.2d 663 (1962)). In this case, the District Court decided important questions of fact and law based entirely on the presentation of a plaintiff who lacked standing. The fact that the United States later "adopted" those findings and conclusions cannot remedy the absence of jurisdiction at trial and in pretrial proceedings.16

In sum, we conclude that because "[t]he right to intervene presupposes an action duly brought," Pianta, 77 F.2d at 890, the intervention of the United States six years into this litigation and after the conclusion of a trial on liability was not sufficient to cure the defect in the District Court's jurisdiction when it entered its findings of fact and conclusions of law on the merits.17

* * *

If a plaintiff lacks standing, the federal "courts have no business deciding [the case], or expounding the law in the course of doing so." DaimlerChrysler Corp. v. Cuno, 547 U.S. 332, 340-41, 126 S.Ct. 1854, 164 L.Ed.2d 589 (2006). Because we agree with defendants that DAI does not have standing and that the intervention of the United States was insufficient to cure that jurisdictional defect, we vacate the judgment and remedial order of the District Court and dismiss the action for want of jurisdiction.

In reaching this conclusion, we are mindful of the possibility that this litigation will continue, inasmuch as the United States—whose standing is not disputed— has represented that, in the event of a dismissal on the basis of standing, it would re-file the action and submit the same evidence at a subsequent trial. Individual plaintiffs with standing could, of course, pursue further litigation as well, either in conjunction DAI or on their own. We are not unsympathetic to the concern that our disposition will delay the resolution of this controversy and impose substantial burdens and transaction costs on the parties, their counsel, and the courts. Should that situation arise, we are confident that the experienced and able district judge, as a consequence of his familiarity with prior proceedings, can devise ways to lessen those burdens and facilitate an appropriate, efficient resolution.

Although we are not presently required to consider the issue of remedy, we do have concerns about the scope of the proposed remedy. If this controversy continues, and if the renewed litigation reaches the remedial phase, the parties and the District Court will have another opportunity to consider an appropriate remedy.

CONCLUSION

To summarize, we conclude that:

The District Court's March 1, 2010 judgment and remedial order is therefore VACATED and the action is DISMISSED for lack of jurisdiction.

Each party shall bear its own costs.