Fig.1 - Legal History of Women in the United States
Like many amazing stories, the history of the Women’s Rights Movement began with a small group of people questioning why human lives were being unfairly constricted.
With the passing of the Equal Pay Act in 1963, from the legal standpoint, it's illegal to pay women less than men simply because they are women.
Source:
https://www.usnews.com/news/the-report/articles/2017-01-20/timeline-the-womens-rights-movement-in-the-us
http://www.nwhp.org/resources/womens-rights-movement/detailed-timeline/