With midterm elections on the horizon, President Obama today took aim at the country's persistent gender wage gap - an issue Democrats see as key to winning-over women voters.

Obama signed an executive order that forces federal contractors to allow employees to discuss their pay with each other. He also signed a presidential memorandum requiring contractors to report pay data based on sex and race to the Labor Department. White House officials said both actions will encourage transparency.

(Credit: Brendan Smialowski/AFP/Getty Images)

"Pay secrecy fosters discrimination, and we should not tolerate it, not in federal contracting or anywhere else," Obama said.

"There are great employers out there who do the right thing, and there are plenty of employers out there who are absolutely certain that there's no pay discrimination happening in their offices, but then sometimes when the data's laid out, it paints a different picture," Obama said. "We want to encourage them to fix these problems, if they exist, by making sure that the data's out there."

The latest U.S. Census statistics show that, on average, full-time working women earn 77 cents to every dollar earned by men nationwide - a gap that has held fairly steady during Obama's presidency.

By other measures, such as comparing men and women in a single type of job or accounting for factors like education and family status, the pay gap is much smaller.

While "secrecy" has been a factor in some pay discrimination, experts say the biggest culprit behind the 77-cent figure is a broader social disparity between women and men in the roles they assume - types of occupations they pursue and income levels they achieve in certain professional fields.

The dynamic is even evident on the White House staff where, according to a recent study by the conservative think-tank American Enterprise Institute whose findings are not disputed by the White House, women earn on average 88 cents to the dollar men make. Administration officials have say women happen to hold more lower-paying jobs in the administration, but deny a disparity in pay for the same work. All federal salaries are public information, and men and women performing the same jobs are paid exactly the same.

"We have as an institution here, have aggressively addressed this challenge, and obviously, though, at the 88 cents … that is not a hundred, but it is better than the national average," White House spokesman Jay Carney said on Monday.

President Obama's executive action on pay equality had significant political overtones ahead of a planned Senate vote on the so-called Paycheck Fairness Act. The Democrat-sponsored legislation would require all employers to prove differences in pay are not based on gender, would force them to allow employees to talk publicly about their wages, and allow lawsuits for punitive damages in cases of alleged sex discrimination.

"I don't know why you would resist the idea that women should be paid the same as men, and then deny that that's not always happening out there," Obama said, ribbing his opponents. "If Republicans in Congress want to prove me wrong, if they want to show that they in fact do care about women being paid the same as men, then show me. They can start tomorrow. They can join us in this, the 21st century, and vote yes on the Paycheck Fairness Act."

Republicans accused Obama of staging a political stunt, saying that pay discrimination is already illegal under existing law and that the proposed measure would unreasonably burden employers.

"All of us support equal pay for equal work," said House Majority Leader Eric Cantor, R-Va. "Let's put the politics aside, and let's get to work to see how we can make sure if there are problems with the law being implemented that we can address that."