Tuesday is Equal Pay Day, marking the disparity between male and female workers in the U.S.

Despite a record number of women entering college and the steady integration of once male-dominated professions, the gender wage gap -- now at 77% -- has budged little in the last four decades.

While the gap in NYC -- a center of high-paid jobs -- is less severe, the repercussions are worse because of the high cost of living.

Christina Thornton, 44, of Hell's Kitchen, prepared for her latest promotion as an executive producer at a major fashion brand by researching the pay for comparable jobs and vigorously data mining industry contacts. "It was just a matter of pushing for what I was due," said Thornton. "New York is a take-care-of-yourself city," said Thornton.

A study by the American Association of University Women showed that one year after graduation, women made about 82% of their male peers, but the pay gap widened through the child-bearing years.

Experts say that many younger women, lacking facts about their employer's pay scale, either do not believe they're being paid less or don't know if they're paid fairly.

That's why equal pay supporters are rooting for Congress to pass the Paycheck Fairness Act, which puts more teeth into the Equal Pay Act of 1963 and prohibits employers from retaliating against workers who ask or talk about salaries. Republicans have vowed to defeat the bill, saying it will reduce workplace flexibility and prompt frivolous lawsuits.

Supporters of more than 40 organizations will converge at City Hall at noon Tuesday to push for passage of the Women's Equality Act, state legislation based on the federal Paycheck Fairness Act, sponsored by Sen. Kirsten Gillibrand.

President Barack Obama is signing an executive order today that will prohibit federal contractors from retaliating against employees who discuss their salaries.

The pay lag has profoundly harmful effects on women, who are more likely to wind up poor after retirement. "My pension would have been higher if I'd pushed for more money," as would her Social Security checks, notes Anne Jackson, 67, a quality assurance tester and computer programmer who recently retired.

The Upper West Sider's reluctance to negotiate, "cost me way more than $100,000" as lost wages have a cumulative effect on savings and the calculation of retirement benefits. But, said Jackson, "in this job market it was just so hard. The older I got the more thankful I was just to have a job." The American Association of University Women and other organizations offer tips and coaching on how women can make a case to management that they are worth more. What holds women back now is less a fault of their negotiating abilities than systemic obstacles, said Dana Britton, director of the Center for Women and Work at Rutgers: "If a woman does something, it's because of who they are: If a man does something, it's a skill they've acquired. When men cook, they're 'chefs' but when women cook -- well, women are just good at cooking."

But further shrinking the pay discrepancy requires policy and legislative changes to accommodate women who need to take time off, limit work hours, or have more flexibility to raise children or otherwise care for the people they love, Britton said.