According to a new study ‘The Gender Pay Gap in Congressional Offices, significant wage gaps exist in the halls of power between men and women — and particularly among Republicans.

Looking at salaries for congressional staffers between 2000 and 2014, the study found that the average gap between men and women was more than $5,500 in the House, and over $7,500 in the Senate. While women constitute 55% of congressional staffers overall, they filled just one-third of senior positions.

Even when women rise to senior positions on the Hill, the wage gaps not only persist but grow. The study found that in the top three positions in each office, gaps reached $10,900 in the House and $9,900 in the Senate.

While the wage gaps exist in both chambers of Congress, the most affected sub-group is women working in Republican offices. According to the study, Republican Congresspeople tend to employ men at a much greater rate in the most senior roles, and for the women who do make it to the top, the gap is 50% larger for female staffers with more than five years of experience in Republican offices.