On the day Philadelphia's new wage-equity law, the first of its kind passed by a U.S. city, was intended to take effect, women's-rights advocates gathered in City Hall to rail against the lawsuit that has sidelined the effort.

"Unless we stand up to the discrimination happening in our workplaces by implementing laws like Philadelphia's wage-equity ordinance, we will not close the wage-equity gap in our lifetimes," said Amal Bass, an attorney with the Women's Law Project.

She called the day "Unequal Pay Day," to highlight the fact that women make on average 79 cents for every dollar made by men.

Legislation passed by City Council in December was intended to address that problem by banning employers from asking job applicants for salary histories. Supporters of the measure say wage disparity starts early in women's careers, then is maintained when women are asked to state their salaries when applying for future positions.

After the legislation passed in Council, the Chamber of Commerce of Greater Philadelphia and Comcast Corp. began privately lobbying against the bill, trying to persuade Mayor Kenney to veto it. When Kenney signed it, the chamber filed suit in early April.

The city has agreed to hold off on enforcing the law pending a judge's decision on whether to grant a preliminary injunction in the case.

The chamber argues the law unfairly limits companies' First Amendment right to free speech. It says free speech can only be limited when there is clear evidence doing so will solve the problem at hand and says banning questions about salary history will not have a clear impact on the gender pay gap.

Councilman Bill Greenlee, the legislation's primary sponsor, said Tuesday he could not address the argument because of the ongoing litigation. He said that in general, too many people have acknowledged the gender pay gap without being willing to try out solutions.

"It is vitally important to show all workers, particularly women, particularly minority women … it's vital to see they are paid for what the position and their experience and their ability dictates," Greenlee said. "It sounds really simple but we haven't quite figured it out."