Equal Pay Act of 1963
The Equal Pay Act of 1963 is a United States labor law amending the Fair Labor Standards Act, aimed at abolishing wage disparity based on sex (see Gender pay gap). It was signed into law on June 10, 1963, by John F. Kennedy as part of his New Frontier Program. In passing the bill, Congress stated that sex discrimination:The law provides (in part) that:
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.”