(a) No employer shall discriminate, within the same establishment in which the employees are employed, between employees on the basis of gender by paying wages to employees at a rate less than the rate at which the employer pays wages to employees of the opposite gender 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 the payment is made pursuant to:
(i) A seniority system;
(ii) A merit system;
(iii) A system which measures earning by quantity or quality of production; or (iv) A differential based on any other factor other than gender.