There is a growing trend in equal-pay legislation to ban employers from inquiring about prospective employees’ salary history. These laws are intended as a remedy to the disparity in pay that follows women throughout their careers, when employers base salaries and raises on what women are already earning—which is often less than their male counterparts. These policies can give women a clean slate when negotiating with new potential employers.

In 2015, California passed an amendment to its equal pay law prohibiting employers from asking candidates about salary history, which took effect this January. In August 2016, Massachusetts passed its own law banning the practice. Philadelphia joined the trend in January of this year, becoming this first city in the nation to pass a law banning the practice of asking prospective employees for past salary information. New York City passed its own ban earlier this month, and Washington, D.C.’s city council is considering a comparable bill.

But businesses are pushing back. Philadelphia’s ban is set to take effect in May, but on April 6, the Chamber of Commerce for Greater Philadelphia filed a lawsuit in U.S. District Court for the Eastern District of Pennsylvania seeking to enjoin enforcement of the law. The Chamber, a vocal opponent of the law, argues that it violates employer’s First Amendment rights to free speech, and does not advance the purpose of closing the gender wage gap. We will monitor developments in this case.