US Senate Republicans blocked a bill that would have made it easier for women to sue their employers to ensure pay equality, a move President Barack Obama called "incredibly disappointing".
With lawmakers voting along exact party lines, the Paycheck Fairness Act introduced by Democrats fell eight votes shy of the 60 necessary to make it to the Senate floor for debate.
"It's a very sad day here in the United States Senate, but it's a sadder day every day when paycheck day comes and women continue to make less than men," Democrat Barbara Mikulski, the longest-serving woman senator and a supporter of the bill, said after the vote.
The White House had been an advocate of the bill, which Democrats said would have strengthened laws against wage discrimination by barring companies from retaliating against employees who voluntarily share pay data with colleagues, and would have made it easier for women to file pay discrimination lawsuits.
"It is incredibly disappointing that in this make-or-break moment for the middle class, Senate Republicans put partisan politics ahead of American women and their families," Obama said in a statement.
"Despite the progress that has been made over the years, women continue to earn substantially less than men for performing the same work," he said.
"My administration will continue to fight for a woman's right for equal pay for equal work, as we rebuild our economy so that hard work pays off, responsibility is rewarded and every American gets a fair shot to succeed."
Senate Minority Leader Mitch McConnell said no Republicans were voting for the legislation because it was merely "about rewarding plaintiff lawyers for filing lawsuits."
"We think it is the wrong way to go about dealing with this issue," he said.
"We have a jobless problem, we have a debt problem, we have a deficit problem," he said.
"We got a lot of problems. Not enough lawsuits is not one of them."
Republicans were largely silent on the issue on the Senate floor Tuesday, except for Nevada's Dean Heller, who introduced a bill that is less comprehensive than Mikulski's.
Senate Majority Leader Harry Reid attacked Republicans for downplaying the problem and blocking "any attempts to try to change the inequities that are out there for everyone to see."
"They want to stick their heads in the sand and ignore the reality that American women experience every day," Reid said before the vote.
Lilly Ledbetter, the woman whose name was attached to prior equal pay legislation that became the first bill signed into law by Obama in early 2009, watched the procedural vote from the Senate gallery.
"This is not right. This country is smarter, we're better than this," she told reporters, as she described the "national epidemic" of paycheck discrimination.
She expressed concern that Mitt Romney, the Republican challenging Obama in November's election, "will not commit to whether or not he would support the Ledbetter bill" requiring fair pay, and warned of a "disaster" should he be elected and seek to repeal it.