Equal Pay Act of 1963
In 1942, Republican congresswoman Winifred C. Stanley from Buffalo, N.Y. introduced H.R. 5056, Prohibiting Discrimination in Pay on Account of Sex, which did not pass at the time. The issue languished until 10 June 1963, when Congress passed the Equal Pay Act ("EPA" or the "Act") as an amendment to the Fair Labor Standards Act, to "prohibit discrimination on account of sex in the payment of wages by employers."
Equal Pay Act and Prior Salary
Prior Salary Information is one of the factors involved in the implementation of the Equal Pay Act and Prior Salary legislation in the United States. 
The Equal Pay Act forbids employers from paying men and women different wages for equal jobs that require equal skill, effort, and responsibility, performed under similar conditions. However, employers can rebut Equal Pay Act challenges by showing that the contested pay differential is based on seniority, merit, quantity or quality of work produced or “any other factor other than sex.” Courts disagree about whether an employee’s prior salary information counts as “any other factor other than sex.”
In the 9th Circuit, prior salary information no longer counts as a factor other than sex, according to a recent case, "Rizo v. Yovino". Specifically, employers can no longer justify the wage differential between male and female employees by relying on their prior salaries, either alone or in combination with other factors. The 9th Circuit reasoned that prior salary is not a legitimate measure of work experience, and that “it may well operate to perpetuate the wage disparities prohibited under the [Equal Pay] Act.”