Equal Pay Act of 1963 - EPA - 29 U.S. Code Chapter 8 § 206(d)

(d) Prohibition of sex discrimination

    (1) No employer having employees subject to any provisions

        of this section shall discriminate, within any establishment

        in which such employees are employed, between employees

        on the basis of sex by paying wages to employees in such

        establishment at a rate less than the rate at which he pays

        wages to employees of the opposite sex in such establishment

        for equal work on jobs the performance of which requires

        equal skill, effort, and responsibility, and which are 

        performed under similar working conditions, except where 

        such payment is 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: 

             Provided, That an employer who is paying a wage rate

             differential in violation of this subsection shall not,

             in order to comply with the provisions of this subsection,

             reduce the wage rate of any employee.

            (2) No labor organization, or its agents, representing

                employees of an employer having employees subject to

                any provisions of this section shall cause or attempt

                to cause such an employer to discriminate against an

                employee in violation of paragraph (1) of this subsection.

            (3) For purposes of administration and enforcement, any amounts

                owing to any employee which have been withheld in violation

                of this subsection shall be deemed to be unpaid minimum

                wages or unpaid overtime compensation under this chapter.

            (4) As used in this subsection, the term "labor organization" 

                means any organization of any kind, or any agency or

                employee representation committee or plan, in which employees

                participate and which exists for the purpose, in whole or in

                part, of dealing with employers concerning grievances, labor

                disputes, wages, rates of pay, hours of employment, or

                conditions of work.