( CNN ) -- Attorneys on both sides of the same-sex marriage debate faced off Monday in a federal appeals court in California , as a panel of judges heard arguments about the constitutionality of Proposition 8 . In August , a federal judge ruled that the voter-approved measure , which defined marriage as a union between a man and a woman , violated the U.S. Constitution . The Ninth U.S . Circuit Court of Appeals considered an appeal of that judge 's ruling Monday . The three-judge panel opened Monday 's hearing with tough questioning of parties seeking to appeal the decision , including ProtectMarriage.com and Isabel Vargas , who 's a deputy clerk and deputy commissioner of civil marriages for Imperial County , California , where voters overwhelmingly approved Proposition 8 . `` What 's your best case to allow for your standing in federal court ? '' one judge asked attorney Charles Cooper , representing ProtectMarriage.com . `` Your honor , I do n't have a case , '' Cooper responded , referring to relevant court cases . Cooper later urged the panel to consider how the California Supreme Court earlier ruled in favor of the voter-approved Proposition 8 . `` If you do n't agree with me that we have standing , '' Cooper told the court , `` then I do urge you to answer the California Supreme Court decision . '' Then Judge Stephen Reinhardt questioned attorney Robert Tyler , who represented Vargas , about how a deputy clerk , instead of the clerk , could have legal standing in the appeal . After a lengthy exchange , Reinhardt appeared frustrated and stated : `` If you do n't know the answer , say so , as the prior attorney did . '' In asserting that his client has standing in the appeal , Tyler told the court that the county clerks are local officers , but they perform state functions such as civil marriages . Monday 's arguments in San Francisco , California , were being divided into two hour-long sessions -- one over the legal standing of those appealing the decision , and one over the constitutionality of Proposition 8 . Monday 's hearing is the latest in a lengthy legal battle over same-sex marriage in California . The state 's high court had allowed same-sex marriage , but then the 2008 Proposition 8 voter referendum passed with 52 percent of the vote . The California Supreme Court subsequently allowed that initiative to stand , saying it represented the will of the people . Two same-sex couples filed a federal challenge , saying the law violated 14th Amendment constitutional protections of due process and equal protection . On August 4 , U.S. District Judge Vaughn Walker agreed , ruling that the voter-approved ban on same-sex marriage violated the equal protection clause of the U.S. Constitution . `` Proposition 8 fails to advance any rational basis in singling out gay men and lesbians for denial of a marriage license , '' Walker , who was appointed to the federal bench by former President George H.W . Bush , wrote in his 136-page opinion . `` Indeed , the evidence shows Proposition 8 does nothing more than enshrine in the California Constitution the notion that opposite-sex couples are superior to same-sex couples . '' Same-sex marriage is currently legal in five states and in the District of Columbia . The five states are Massachusetts , Connecticut , Vermont , Iowa and New Hampshire . Walker 's landmark ruling led to a swift federal appeal that could ultimately reach the Supreme Court .
NEW : Judges ask tough questions to side opposing same-sex marriage . A panel of judges will hear arguments over whether the measure is constitutional . A lengthy legal battle continues after voters approved Proposition 8 . Score: 6