Mikulski pointed out that this has been a 50-year battle since the Equal Pay Act was passed in 1963. The senators said that despite that bill, women still make 77 cents for every dollar their male counterparts do for the same job, which costs women more than $400,000 throughout their lifetime.

“We pay the same for food, we pay the same for gas and we pay the same for the mortgage even though we’re getting paid less,” Stabenow said. “That’s just not right.”

Cantwell said that Democrats would work “hard” during the 113th Congress to pass the Paycheck Fairness Act, S. 84, which would also provide a grant program for women in the workplace to be trained on how to negotiate for their salaries.

“We made a big step forward with the Lilly Ledbetter Fair Pay Act but we need to continue to make progress by passing this important legislation,” Cantwell said.

Nearly four years ago, President Obama signed his first bill into law — the Lilly Ledbetter Fair Pay Act, which allows women to sue employers for back pay if they were discriminated against.

The Paycheck Fairness Act would amend the Fair Labor Standards Act of 1938 which now says employers cannot offer different salaries on the basis of sex. The bill would further clarify the law to say discrimination can only happen due to a "bona fide factor other than sex, such as education, training, or experience."

The bill prohibits employers from retaliating against workers who share their salary information with their coworkers, and increases penalties against employers who violate the law. Those penalties can be compensatory damages, or punitive damages in some cases, except the United States government is exempt from these punitive damages.

Elsewhere, the bill creates an award that can be given to employers for pay equity, and would require the Employment Opportunity Commission to survey available data on employee pay information "for use in the enforcement of Federal laws prohibiting pay discrimination." That data should also help the Commission decide "additional data collections that will enhance the enforcement of such laws."

Based on that survey, the Commission would then issue regulations "to provide for the collection of pay information data from employers as described by the sex, race and national origin of employees."

The bill authorizes $15 million in new spending. A similar bill last year failed to move in the Senate, after senators voted 52-47 against ending debate — 60 votes were needed to advance the bill.

Boxer said she doesn’t understand why Republicans have filibustered this bill in the past.

“We’re calling on [Republicans] in the spirit of fairness and justice to give all the women in America the same opportunity as their male counterparts,” Boxer said. “If there is [another] filibuster to this bill, I will not understand it.”

Pete Kasperowicz contributed to this article.