In a showdown expected Wednesday, Senate Republicans seemed likely to derail the measure. Though Democrats run the chamber, they control 55 votes and needed at least five Republicans to halt a GOP blockade against it — a number they seemed unlikely to reach.
The battle was suffused with the politics of an election year in which Republicans could capture Senate control and are expected to retain their hold on the House. Senate Republicans derailed the bill in 2010 and 2012, the last two election years.
Democrats all but dared Republicans on Tuesday to resist the legislation, which would make it harder for companies to pay women less than men for the same work and easier for aggrieved workers to sue employers.
"Republicans stand opposed to pay equity at their own peril," said Sen. Chuck Schumer of New York, the No. 3 Senate Democrat. He pointedly added, "We're going to come back to this issue several times this year."
Countered Sen. John Thune of South Dakota, a member of the GOP leadership, "It's very clear what this is about, and that is very simply trying to score political points."
In a year when polls show little enthusiasm among Democratic voters, congressional Democrats were using the fight to beckon to women, who generally favor the party. Hoping to broaden its appeal, they also cast the issue as a crucial one for the middle class because so many families rely on female wage-earners.
Republicans, with strong backing from the U.S. Chamber of Commerce and other business groups, said the measure would tie the hands of employers. They proposed alternatives that would cut taxes, allow more flexibility for workers' hours and take other steps to help companies.
Joined by Democratic lawmakers and Lilly Ledbetter at the White House, President Barack Obama took a swipe at the GOP. Ledbetter's claims of pay inequity by her employer led to the 2009 anti-discrimination statute bearing her name, the first bill Obama signed as president.
"Republicans in Congress have been gumming up the works. They've been blocking progress on this issue," said Obama, adding later: "America, you don't have to sit still. You can make sure that you're putting some pressure on members of Congress about this issue."
Obama issued an executive order prohibiting federal contractors from retaliating against workers who discuss their pay. He also ordered the Labor Department to write rules requiring federal contractors to provide compensation data by race and gender.
Republicans said the bill would make it hard for companies to award merit pay or offer flexible work hours in exchange for lower pay and expose employers to costly, frivolous lawsuits.
Minority Leader Mitch McConnell, R-Ky., cited statistics showing how women's income has fallen and their poverty rate increased under Obama.
"It's important to kind of put in place the record of the current administration with regard to women," McConnell said. Obama took office during the worst recession since the Great Depression of the 1930s.
As if to underscore the political sensitivity of the debate, McConnell held his usual Tuesday session with reporters accompanied only by Sen. Deb Fischer, R-Neb., who was pushing a narrower version of the legislation. Typically, McConnell faces the cameras joined by the top members of the Senate GOP leadership, who are all men.
At almost the same time, a parade of Democratic female senators trooped to the Senate floor to defend the bill.
"We want the same pay for the same job, and we want it in our law books and we want it in our checkbooks," said Sen. Barbara Mikulski, D-Md., the measure's chief sponsor.
Mikulski's bill would narrow the factors businesses can cite for paying women less than men in the same jobs, and bar employers from retaliating against workers who share salary information. It also would make it easier to bring class-action lawsuits against companies and let victors in such lawsuits win punitive and compensatory damages.
Paycheck discrimination based on gender has been illegal since the 1960s. The Ledbetter law extended the time people have to file lawsuits claiming violations of that law.
Women averaged 77 percent of men's earnings in 2012, according to Census Bureau figures. That is better than the 61 percent differential of 1960, but little changed since 2001.
While few deny workplace discrimination exists, politicians and analysts debate its impact on women's earnings.
Data shows that men tend to out-earn women at every level of education and in comparable jobs.
Yet women generally work shorter hours and are likelier to take lower-paying jobs. Sixty-two percent of the 3.3 million workers earning at or below the minimum wage last year were women, according to the federal Bureau of Labor Statistics.
Even if the Democratic bill emerges from the Senate, it appears to have little chance in the GOP-run House.
"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," said House Majority Leader Eric Cantor, R-Va., on Tuesday.
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