Employers should not have authority under federal workplace laws to use prior salary history to justify paying male and female workers differently for the same roles, a California lawyer told the U.S. Supreme Court on Wednesday in a closely watched case confronting a common employment practice.

The case Fresno County Superintendent of Schools v. Rizo, which arrived in March from the U.S. Court of Appeals for the Ninth Circuit, is a fresh test of the scope of the federal Equal Pay Act, or EPA. The Ninth Circuit’s ruling against the school district said the equal pay law required employers to base any wage disparities on job-related factors other than sex.