The U.S. Court of Appeals for the Ninth Circuit will revisit a pay-equality ruling that federal officials and advocacy groups argued would widen and institutionalize practices that allow women to be paid less than men based on past salaries.

The en banc court is set to hear the case in December. A three-judge panel in April said pay discrepancies exclusively based on previous salary are not discriminatory under the Equal Pay Act, which forbids employers from paying women less than men. The court said an employer could base a salary on previous pay if it shows its use was “reasonable and effectuated a business policy.”

The U.S. Equal Employment Opportunity Commission called for the Ninth Circuit to rehear the case. The agency noted a split among earlier appeals court rulings and said there would be wide and harmful effects in closing the gender pay gap in the United States, where research shows women make 80 cents on the dollar compared to male counterparts.

“If, as the panel holds, employers may base starting pay on what employees earn in their previous jobs, women on average will continue to earn less than men for substantially equal work,” the EEOC argued in court papers. Rather than eliminating an existing gap, such a policy, the agency said, would perpetuate it. 

Special Report: The Push for Pay Equity

In 2012, Aileen Rizo, who worked for a Fresno County, California, public school, sued her employer after she discovered her male co-workers were making higher salaries despite comparable or equal experience. Rizo complained to human resources, according to court papers, but her lawyers said officials “refused to take any action to rectify the pay disparity.” The Oakland law firm Siegel & Yee represents Rizo.

The county’s standard policy for hiring added 5 percent to previous pay and then bumped her up to the minimum for her position at $63,000. Male colleagues with similar experience made as much as $10,000 or more than she earned, according to her complaint.

Fresno’s lawyers at the firm McCormick, Barstow, Sheppard, Wayte & Carruth told the California trial judge in court papers: “A man in the exact same circumstances as plaintiff would have started at the same initial salary as plaintiff.”

The Equal Pay Act creates exceptions when pay is based on seniority, merit, quantity or quality of work or “any other factor other than sex.”