No employer having employees 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. For purposes of administration and enforcement, any amounts owing to any employee which have been withheld in violation of this section shall be deemed to be unpaid wages or unpaid overtime compensation and the employee whose wages have been wrongfully withheld in violation of this section shall have a right of action therefor to recover damages to the extent of two times the amount of wages so withheld. This section shall not apply to employers covered by the Fair Labor Standards Act of 1938 as amended. Every action under this section shall be brought within two years next after the right to bring the same shall have accrued; provided, however, that nothing herein shall be construed to give rise to a cause of action for work performed prior to July 1, 1974.