As President Barack Obama and the Democrats prepare to honor "Equal Pay Day," Senate Democrats continue to pay female employees significantly less than their male counterparts, according to an analysis of Senate salary data in Democratic offices.

Senate Democrats plan to vote on the Paycheck Fairness Act on Tuesday, though the vote is largely symbolic given the unlikelihood that the bill will be brought to the floor of the Republican-controlled House.

Democrats have a lot of work to do in their own offices, according to an analysis of salary figures compiled from secretary of the Senate reports covering the fiscal year 2013.

Senators who were not in office for the entirety of the fiscal year were not included in the analysis. Staffers that were not employed for the entire year were also excluded from calculations.

The analysis shows female staffers in Democratic Senate offices were paid just 91 cents for each dollar paid to male staffers. The average salary for a woman was more than $5,500 below the average salary for a man.

Men received higher average salaries in more than two-thirds of the 43 Senate offices analyzed.

Many of the senators with the largest pay disparity between men and women are facing reelection battles in 2014.

Among those with the greatest disparity is Sen. Mark Warner (D., Va.), who paid his female staffers only 72 cents on the dollar compared to male staffers. The average female salary was $20,861 below the average male salary.

Alaska’s Sen. Mark Begich (D.) was even tougher on his female staffers. He paid his female employees just 71 cents on the dollar, for a gender pay gap of $23,504.

Sen. Mary Landrieu (D., La.), who just last week held a press conference on the issue of equal pay, was also found to pay her female staffers far less compared to males. The average male salary was $13,037 higher than the average female salary. Women made just 82 cents for each dollar made by men.

Numerous senators up for reelection have an especially large gap between male and female salaries:

Sen. Kay Hagan (D., N.C.): $15,343 higher average male salary;

Sen. Mark Udall (D., Colo.): $9,783 higher average male salary;

Sen. Jeanne Shaheen (D., N.H.): $6,267 higher average male salary;

Sen. Mark Pryor (D., Ark.): $5,799 higher average male salary;

Sen. Jeff Merkley (D., Ore.): $3,189 higher average male salary.

This is not a new problem for Democrats. A previous Washington Free Beacon analysis of the fiscal year 2011 found that Democratic Senate offices were paying female staffers far less than their male coworkers during that year as well.

Women were also paid less than men at the Democratic National Committee, in Obama’s White House, and on his 2012 presidential campaign.

Sen. Bernie Sanders (I., Vt.), who caucuses with the Democrats, was the worst of the gender pay gap offenders in the previous analysis. He remains near the bottom of the list, with the average female salary $21,730 lower than the average salary received by men in his office.

The Democratic Senatorial Campaign Committee (DSCC) plans to push hard against Republicans on Tuesday for "Equal Pay Day," launching ads on the web, Twitter, and Facebook.

The hashtag "#GOPPayGap" will be used to highlight Republicans who have voiced their opposition to equal pay.

"The DSCC’s ‘GOP PAY GAP’ campaign will hold Republican Senate candidates accountable for their baseless and partisan opposition to equal pay for equal work," said DSCC spokeswoman Regan Page.