In 2013, female staffers in congressional offices were paid 91 cents for every dollar that men made in the House and 88 cents for every dollar men made in the Senate, according to an analysis of staff salary records by LegiStorm.
The gender gap among Republican staffers was greater than the gap among those working for Democrats. Republican House female staffers made 84 cents for every dollar made by Republican House men, while House Democratic women made 99 cents for every dollar made by their male counterparts, the report said.
In the Senate, Republican female staffers made 85 cents for every dollar made by Senate GOP men, while Democratic women in the Senate made 92 cents for every dollar made by Senate Democratic men, said LegisStorm, a Congress-focused research group.
The White House has said women in the national workforce on average earn only 77 cents for every dollar a man makes. But many have disputed the number, saying it doesn't take into account job descriptions and hours worked.
Republicans on Wednesday blocked a Democratic bill that would have required companies to prove that wage discrepancies aren't based on gender.
Current law already bans gender-based pay discrimination. The Senate bill would have further equipped the Labor Department to find cases of wage disparity suffered by women and minorities, and it would have made it easier to file lawsuits and receive huge payouts from companies found guilty of such discrimination.
Gender wage discrimination doesn't exist for members of Congress, as the annual salary for senators and representatives is $174,000. Only the speaker of the House ($223,500) and the Senate president pro tempore and Senate majority and minority leaders ($193,400) earn more.