Appellant Bernice P. Goodrich brought this civil action against her employer, the International Brotherhood of Electrical Workers ("IBEW"), pursuant to the Equal Pay Act of 1963.1 The Act targets an "endemic problem of employment discrimination"; it is a "broadly remedial" statute, which firmly establishes as federal law the "principle of equal pay for equal work regardless of sex." Corning Glass Works v. Brennan, 417 U.S. 188, 190, 195, 208, 94 S. Ct. 2223, 2228, 2234, 41 L. Ed. 2d 1 (1974).2 Goodrich alleged that she performs the same work as a number of male IBEW employees, but is paid substantially less.

The IBEW sought summary judgment on two grounds. First, it asserted that Goodrich and the male employees in question did not perform "equal work." Second, it relied on the Act's awkwardly-phrased fourth affirmative defense: the wage disparity at issue, the IBEW urged, was "based on any other factor other than sex." 29 U.S.C. § 206(d)(1)(iv) (1976). The district court found that genuine issues of material fact precluded summary adjudication of the "unequal work" defense, but held that the IBEW was entitled to judgment, as a matter of law, on its "other factor other than sex" plea.

Our review indicates that the district court applied the Act's residuary affirmative defense incautiously and disposed of the case precipitously. As explained by the IBEW, both the unequal work plea and the residuary defense ultimately rested on the same contentions--that the men with whom Goodrich compared herself were on call to perform additional duties and had special expertise augmenting the value of their services to the union. The district court correctly ruled that the IBEW's "additional duties" and "special expertise" contentions entailed disputed matters of fact relevant to a determination whether Goodrich and her male co-workers were engaged in equal work. When the same contentions reappeared in explanation of the IBEW's "other factor other than sex defense," however, the district court viewed them differently and granted summary judgment. We conclude that the "additional duties" and "special expertise" contentions present triable issues. We therefore reverse the judgment entered summarily for the IBEW, and remand the case for further proceedings.I. BACKGROUND

Bernice Goodrich has been employed at the IBEW's headquarters in Washington, D.C. since 1952; she is not, however, a union member. In 1961, she began work at her present position as an "agreement analyst" in the agreement approval department. The primary function of the department is to review labor agreements that local unions submit to the International President for his approval.

The department is headed by a director, who is male, and has a professional staff of six employees, five males and Goodrich. Of the six staff members, only Goodrich is classified as an agreement analyst. The five male employees hold the position of either "International Representative" or "Senior International Representative." The two "International Representative" classifications carry a large financial advantage. Although Goodrich has considerably more experience in reviewing labor agreements than any of her male colleagues,3 she receives substantially less pay.4

International Representative status at the IBEW's headquarters is entirely dependent upon active membership in the union. All professional employees at the union's headquarters who have been active members of an IBEW local hold the International Representative title. And only active union members, pursuant to the IBEW "membership rule," are eligible for designation as International Representatives. The agreement approval department is one among many areas of the union's professional operations in which International Representatives work. Regardless of the particular jobs they hold, International Representatives receive a uniform annual salary based on their seniority in the union. These salaries are generally much higher than those paid to professional employees who are not union members. Thus, despite Goodrich's extensive experience in the agreement analysis department, she is paid less than her male co-workers because she has never been a union member and is therefore ineligible to be an International Representative.

In December 1981, Goodrich commenced this action claiming that the disparity between her pay and that of her male co-workers violated the Equal Pay Act. To establish a prima facie case under the Act, a plaintiff must show that an employer pays different wages to employees of opposite sexes "for equal work on jobs the performance of which requires equal skill, effort, and responsibility, and which are performed under similar working conditions." 29 U.S.C. § 206(d)(1) (1976); see Corning Glass Works v. Brennan, 417 U.S. 188, 195, 94 S. Ct. 2223, 2228, 41 L. Ed. 2d 1 (1974) (legislative history clarifies that plaintiff must make these threshold showings). Once a plaintiff has carried this initial burden, a defendant may escape liability either by refuting any part of the prima facie case, or by pleading and proving one of the Act's four affirmative defenses. These defenses permit payment of different wages if "made pursuant to (i) a seniority system; (ii) a merit system; (iii) a system which measures earnings by quantity or quality of production; or (iv) a differential based on any other factor other than sex." 29 U.S.C. § 206(d)(1) (1976).5

In her complaint, Goodrich alleged the necessary elements of a prima facie violation of the Act. The parties then stipulated, inter alia, that: (1) the work performed by Goodrich is equal to the work of the five male International Representatives "at such times as such Representatives are assigned to and physically performing work in the Agreement Approval Department"; (2) the IBEW has always required active union membership as a prerequisite to International Representative status; and (3) the "membership rule" has been applied equally and without exception to male and female IBEW employees. Record Excerpts (R.E.) 14-15.

The IBEW initially challenged Goodrich's prima facie case by arguing that the work she performed was not equal, within the meaning of the Act, to the work International Representatives performed. The Equal Pay Act standard is neither "comparable" work nor "identical" work. Instead, the test under the Act is "substantial equality"--whether the jobs in question are substantially related and substantially similar in skill, effort, responsibility, and working conditions. See Thompson v. Sawyer, 678 F.2d 257, 274 (D.C.Cir.1982); Laffey v. Northwest Airlines, Inc., 567 F.2d 429, 449 (D.C.Cir.1976), cert. denied, 434 U.S. 1086, 98 S. Ct. 1281, 55 L. Ed. 2d 792 (1978). According to the IBEW, the work in this case was unequal for two reasons: International Representatives perform additional duties beyond those required for the particular jobs they currently hold, and they have special expertise relevant to their duties.6 Goodrich contested these claims; she asserted that the additional work was trivial, frequently nothing more than attending social functions, and that the alleged special expertise had no relationship to the work performed at headquarters.7 The district court concluded that the parties' conflicting allegations concerning the "substantial equality" of the work performed by Goodrich and males in the agreement approval department presented material issues of fact that were not appropriate for resolution by summary judgment. Memorandum Opinion (Mem. Op.) at 3, R.E. 8.

As a second defense, the IBEW asserted that any wage disparity rested upon a bona fide factor other than sex--the fourth affirmative defense under the Act. The union identified its membership rule, which precludes Goodrich from becoming an International Representative, as the requisite neutral factor. Significantly, however, the IBEW did not assert that the additional pay International Representatives received was principally a bonus in recognition of important service rendered to locals in past years. Instead, the union claimed that the membership rule served to assure that International Representatives would have the special expertise required for the additional duties they perform. Goodrich repeated in this context what she had said in relation to the "unequal work" defense. She contended that the membership rule in fact does not serve the alleged purpose because special expertise in local union problems is not needed in the jobs her co-workers hold and the extra duties, to the extent they exist, are insubstantial.

The district court believed the stipulation that the membership rule is applied equally to men and women doomed "any attempt [by Goodrich] to draw [the IBEW's] affirmative defense into question." Mem. Op. at 4, R.E. 9. The IBEW, according to the district court, had "carefully and extensively explained its position that the union membership rule is a bona fide rule that serves a valuable business purpose." Id. at 6, R.E. 11. Despite Goodrich's argument that the expertise relevant to job performance and additional work claims lacked solid evidentiary support, so that the alleged "valuable business purpose" had not been established as a matter of law, the district court remarked that Goodrich "made no attempt to rebut defendant's justification for the IBEW membership rule." Id. On this reasoning, the district court granted the IBEW's motion for summary judgment.

In essence, the district court held that "additional duties" and "special expertise" contentions can do double duty. If proved, they can defeat a claim that the employees in question are engaged in equal work. But they can serve as well to establish that a rule not framed in terms of sex, such as the IBEW membership rule, is bona fide. However, under the district court's view of this case, "additional duties" and "special expertise," when pressed into service in this latter fashion, can carry the day for the employer if the contentions are merely alleged; under the residuary, fourth affirmative defense, the contentions need not be proved.

We believe this view of the breadth of the residuary defense would substantially undermine the equal pay principle advanced by the Act. "Additional duties" and "special expertise" contentions, we hold, do not establish that a rule or criterion is bona fide when those contentions merely restate "unequal work" assertions which involve genuine issues of fact.

Case law, citing the Equal Pay Act's legislative history, establishes that the residuary affirmative defense applies only when "pay differentials are based on a bona fide use of 'other factors other than sex.' " County of Washington v. Gunther, 452 U.S. 161, 170, 101 S. Ct. 2242, 2248, 68 L. Ed. 2d 751 (1981) (emphasis added).8 The IBEW here relied on its "additional duties" and "special expertise" explanation to justify as bona fide use of the membership rule to establish pay differentials that, in Goodrich's case and perhaps generally, separated women from men.9 We do not determine whether a different rationale for the higher pay awarded International Representatives would have been subject to trial. See supra pp. 1492-1493. We hold only that when "additional duties" and "special expertise" are the factors ultimately relied upon,10 the residuary defense11 will not serve to avoid the trial that would be required to test whether the alleged extra duties and expertise exist and mark the work in question as unequal.

In the further proceedings our remand requires, we caution the district court against overreading the parties' stipulation. That court commented: "Although [Goodrich] may not have foreseen the legal effect of her stipulation, it forecloses [her] from contending that the IBEW membership requirement constitutes sex-based wage discrimination." Mem. Op. at 4-5, R.E. 10-11. Fairly construed, the stipulation simply acknowledged that the IBEW has consistently adhered to the membership rule, that the rule is longstanding, and that it bars males who lack union membership, as it bars females who are not union members, from achieving International Representative status.

A concession as to the length of time a rule has remained in place and the employer's consistency in adhering to it is not a concession that the rule insulates the employer from Equal Pay Act liability. See Thompson v. Sawyer, supra, 678 F.2d at 277 ("longstanding" binding industry practices are not bona fide factors other than sex because they constitute a "continuing structure of sexual discrimination"). Nor is a plaintiff barred from contesting the genuineness of the reasons an employer proffers for a rule (here, to provide compensation for additional duties and special expertise) because the rule itself does not invoke a sex criterion or because the plaintiff has not attempted to bring herself within the rule. See Corning Glass Works v. Brennan, supra, 417 U.S. at 203-05, 209-10, 94 S. Ct. at 2232-33, 2235; Thompson v. Sawyer, supra, 678 F.2d at 276-77, aff'g in relevant part Thompson v. Boyle, 499 F. Supp. 1147, 1158-59, 1166 (D.D.C.1979).12

Under the familiar standard leading us to remand this case, a party seeking summary judgment must demonstrate that there is no genuine issue of material fact and that he or she is entitled to prevail as a matter of law. Fed.R.Civ.P. 56(c). In determining whether a genuine issue exists, the trial court must accord the party opposing the motion the benefit of all reasonable doubts, and construe matters presented in connection with the motion most favorably to the motion's opponent. See, e.g., McSurely v. McClellan, 697 F.2d 309, 321 (D.C.Cir.1982) (per curiam); Abraham v. Graphic Arts International Union, 660 F.2d 811, 814 (D.C.Cir.1981).13

Viewing the record before us in the light most favorable to Goodrich, and bearing in mind that reasonable doubts must be resolved against the IBEW, we are persuaded that the union has not sustained its summary judgment burden. Goodrich has raised factual issues relevant to determining whether the IBEW has paid her less than it pays employees of the opposite sex engaged in substantially equal work. She has called into question the genuineness of the IBEW's claims that her male co-workers merit higher pay because, as International Representatives, they perform additional duties and have relevant special expertise. To defeat summary judgment for the union, Goodrich was required to do no more.

For the reasons stated, we reverse the judgment from which this appeal has been taken and remand the case to the district court for further proceedings consistent with this opinion.

It is so ordered.