No, generally speaking, not if the restroom is not for use by the general public.

Nevertheless, you should make your best efforts to make the restroom ADA accessible because your business could still be sued for accessibility violations. If you are leasing the retail space, talk to your landlord.

The best person to advise you regarding ADA compliance is a CASp. CASp is short for “Certified Access Specialists”, which is a new professional title in California created as a result of California’s Construction-Related Accessibility Standards Compliance Act (Civil Code §55.51, et seq.).

Based on Senate Bill 1608, the Construction-Related Accessibility Standards Compliance Act became effective in California on January 1, 2009. The law was designed to encourage businesses and property owners to make their places of public accommodation more accessible by rewarding compliance.

After the CASp determines that a business meets applicable construction-related accessibility standards and issues a report of that determination, the business is permitted to display a CASp-issued numbered, watermarked “Disability Access Certificate.”

By obtaining certification from a Certified Access Specialist or CASp, the building and/or business is granted “special legal rights" if later sued in an accessibility lawsuit. Upon application by a “qualified defendant" (business owner who obtained a determination of compliance from a CASp), the court will issue a 90-day stay of the accessibility claim, and to schedule a mandatory early evaluation conference at which both parties must appear in person. Although the stay and the early evaluation conference procedure is not a "right-to-cure" period nor is it a "safe harbor", it is designed to reduce litigation expenses for defendants of accessibility lawsuits.

Note that a CASp inspection and report does not bind the court and does not affect the court’s ultimate authority to make findings of fact and law. Nor does the CASp inspection and report prevent recovery of damages by a person with a disability who is personally or actually deterred from accessing a place of public accommodation because of an access violation.

The bathroom must be ADA compliant ONLY if it is for public and/or common use. Public use describes interior or exterior rooms or spaces that are made available to the general public. Public use may be provided at a building or facility that is privately or publicly owned.
Common use refers to those interior and exterior rooms, spaces, or elements that are made available for the use of a restricted group of people (for example, occupants of a homeless shelter, the occupants of an office building, or the guests of such occupants).

Arguably, since you are restricting use to the your three employees (assuming they do not have ADA needs for special accommodations), the bathroom is likely exempt from ADA requirements.