At this very moment, President Obama is preparing to sign the Lilly Ledbetter Fair Pay Act into law. It's an admirable bill that remedies a regrettable 2007 Supreme Court ruling which had constrained the time limit for women to file pay-discrimination claims against their employers.

Media coverage of today's White House ceremony depicts the Ledbetter signing as a major victory for gender pay equity. But a much broader bill addressing pay discrimination -- the Paycheck Fairness Act -- faces a mysteriously uncertain future in the Senate, where it has yet to receive a floor vote despite approval in the House last year and again this year.

What's the holdup? And will the (well-deserved) hoopla over the Ledbetter victory obscure the facts behind the inaction on Paycheck Fairness?

When the House passed the Ledbetter measure, which deals narrowly with the Supreme Court ruling in Ledbetter v. Goodyear, it combined that bill with the Paycheck Fairness Act (PFA), which would refine the 1963 Equal Pay Act in several major ways.

In addition to making it easier for women to file class action suits alleging pay discrimination, the PFA would require employers to meet a burden of proof when alleging that unequal pay for female workers is justified by a "factor other than sex." Women would also become eligible under the bill for compensatory damages when they prevail in wage discrimination suits. Before his election last year, Obama was a co-sponsor of the PFA, which was championed by now-Secretary of State Hillary Clinton.

So now that Obama's in the White House, and Democrats have greater majorities in the House and Senate, one would think that the PFA had a better chance of making it into law today. The Hartford Courant reported last week that Rep. Rosa DeLauro (D-CT), the bill's House-side champion, expects it to be passed by springtime.

But in Washington, issues often get starved of attention after one victory is achieved and a resting-on-laurels mentality sets in. And we know who's rooting for the PFA to fall by the wayside: K Street.

In 2007 testimony "strongly oppos[ing]" the PFA, the U.S. Chamber of Commerce suggested that pay inequity exists because of women's "personal choice" and their propensity to take on parenting duties:

The proponents of the Act have not cited any evidence establishing that the existing wage gap is caused by employer discrimination. ... As labor economists and feminist scholars alike have proven and observed, the existing wage gap between men and women is attributable to a number of factors ... includ[ing]: personal choice; women's disproportionate responsibilities as caregivers and other family obligations; education; self-selection for promotions and the attendant status and monetary awards; and other "human capital" factors.

Late Update: In its statement on the Ledbetter signing, the ACLU made sure not to forget Paycheck Fairness. From counsel Deborah J. Vagins:

The Lilly Ledbetter Fair Pay Act rights the wrong done by the Supreme Court in Ledbetter v. Goodyear. With this law, people who have suffered pay discrimination can once again seek vindication without facing unduly and unfairly restrictive deadlines. Now that Congress and the President have restored access to the courthouse, it is time to close the loopholes that make wage discrimination possible by passing the Paycheck Fairness Act.

Later Timeframe Update: Sen. Barbara Mikulski (D-MD), the Ledbetter bill's champion and a potential new leader on the Paycheck Fairness Act, has said the Senate could take action on the PFA as soon as the spring.

Jocelyn Samuels, vice president for education and employment at the National Women's Law Center, agreed. "There are any number of champions for fair pay in the Senate who, I think, recognize that while the Ledbetter bill is a fabulous down payment on ensuring pay equity for women, we need to do more than restore prior law [as the Ledbetter bill does] -- we need to move it forward," she told me.

Asked about the opposition from the Chamber and other employer groups, Samuels stressed the importance of educating senators and the public about the realistic possibility for punitive damages awarded under the PFA.

"Some of the concerns that have been expressed about the bill have been really misinformed," she said. Under the PFA, women who can meet the burden of proof for wage discrimination based on gender are allowed the same opportunity to collect court damages as those subjected to racial or ethnic discrimination.

Kim Gandy, president of the National Organization for Women, said the House packaged the Ledbetter bill with the PFA "for a reason"; namely, the desire to use the momentum of the better-known former to help propel the lesser-known latter measure to passage. "It's a little harder without that moving train," she added, "but there's no reason they can't or won't pursue it [in the Senate]."