The question before a federal appeals court last week centeredaround a common hiring practice that women's rightsadvocates say perpetuates the gender wage gap: whether or not an employer'suse of prior salary to determine wages unfairly justifies paying women less than men.

Attorneys sparred before the en banc U.S. Court of Appeals forthe Ninth Circuit, which considered the case that Aileen Rizo, a mathconsultant in Fresno County, California, filed in 2012. Rizo suedafter she discovered she was paid less than male counterparts by asmuch as $10,000. The county justified the pay differential based on the previous salaryshe made at a school in Arizona.

A three-judge panel in April ruled the prior salarycould be used to justify the pay gap. The U.S. Equal EmploymentOpportunity Commission and other women's rights advocateshad urged the court to reconsider thatdecision, saying that any validation of such a practice wouldinstitutionalize the gender pay gap. Studies show women make 80cents on the dollar to their male counterparts and that thedisparities are pervasive across industries.

Several cities and states have banned salary historyinquiries. California's new law, which takes effect inJanuary, bans private and public employers from asking about acandidate's pay history. It shifts the power, as well, allowingemployees to ask about what the potential salary range would be fora position.

Delaware, Massachusetts, Oregon, New Orleans, Philadelphia,Pittsburgh, New York City and Puerto Rico also have existing orpending bans on requesting salary history for either all employersor just public.

The courts have moved in different directions. Two federalappeals courts—the Tenth and Eleventh circuits—previously held thatprior pay alone cannot be considered as an exemption to equal paylaws. The Seventh Circuit has ruled that previous salary could beconsidered.

Women's and civil rights groups, closely tracking the case inthe Ninth Circuit, weighed in with friend-of-the-court briefs thaturged the court to overturn the panel ruling. These included theEEOC, the National Women's Law Center and the American CivilLiberties Union. Several management groups said the court shoulduphold the panel's position. Watch the argument video here:

Jones Day partner Shay Dvoretzky, representing Fresno County'ssuperintendent and Office of Education, argued the Equal Pay Actallows employers to consider “any factor other than sex” indetermining salaries. He argued prior salary was a gender-neutralfactor.

An employee's use of prior salary is a reasonable businessconsideration, Dvoretzky argued. He said, in response to questionsfrom the panel, that the Equal Pay Act doesn't require an employerto “catch up” or equal salaries or address disparities across thecompany.

Many of the judges expressed skepticism to Dvoretzky'sarguments.

“My broader question is: The basic purpose of the Equal Pay Actis to correct imbalances in the market based on gender,” said JudgeWilliam Fletcher. “It seems counterintuitive to the function of thestatute to allow it to feed back into the pay setting, the set ofpay differentials that the statute is designed to protect.”

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Dvoretzky also argued the evidence did not show Rizo was paidunequally in her previous job or that there was discrimination.

“You're looking at it in terms of whether this decision was madeon sex-based salary but that's not the question,” Judge MarshaBerzon said. “What did Congress mean when it passed thestatute?”

Attorneys for the other side were questioned on the scope ofbanning prior salary, and the judges attempted to nail down theirstances and also to point to whether salary history could beisolated in the pay gap data to prove causation.

Rizo's attorney, Daniel Siegel at Oakland-based Siegel &Yee, EEOC's Barbara Sloan and Equal Rights Advocates attorneyJessica Stender contented that prior salary cannot be used asa justification for pay, but it can be used in some instances in acombination of factors, which confused the judges.

“You can rely on what the salary represents but not the salary,”Berzon said in response.

'Another world'

Siegel added, in response to a question about whether salarycould be considered in a world with no gender pay gap, “If we couldno longer demonstrate that prior salary was a proxy for sex bias, Ithink we'd be in another world. I don't think it would be two yearsfrom now, it could be 30 years from now.”

Reinhart said job experience and education related to the job isrelevant in determining salary, not former pay. Other judges alsopinned down the question of when prior salary could be used indetermining pay scale.

Stender argued it was inherently sex-based to rely on priorsalary without any other factor to justify unequal pay for equalwork. She added a caveat when questioned where she said employerscan use the information of prior salary to entice a job applicantwith a significant pay raise.

Sloan of the EEOC walked a fine line, as well, and was notunequivocal and also said that prior salary could be part of a“bundle of things that goes into the mix.”

“I think Congress' intent was to eliminate the pay gap, but I'mnot sure that it says prior pay is a proxy for sex discrimination,”Sloan said.

She added later, however, that prior salary can lead to a cycleof lower pay and disparity. She said that prior pay cannot causethe disparity.

If prior salary is relied upon, she said, “How would they everget caught up? That's the problem. Once you consider it, you end upin a box.”