Justice Seamus McCaffery's question prompted a ripple of laughter from the audience in the courtroom in Philadelphia's City Hall, The Philadelphia Inquirer reported.
McCaffery, a Democrat, had a short question: "Could there be politics, maybe?"
Pennsylvania, carried by President Barack Obama in 2008, appears to be a swing state this year. Mike Turzai, majority leader of the state House of Representatives, told a meeting of fellow Republicans weeks ago that the stringent law requiring voters to show photo identification would allow Republican nominee Mitt Romney to carry the state.
Opponents of the law, who have already lost before a lower court, have asked the high court to grant an injunction that would keep the law from being implemented during the November election.
David Gersch, representing the challengers, told the court the law's backers have produced no instance of actual in-person voter fraud. He said Pennsylvania has not allowed enough time to ensure all voters who require it get photo ID.
A lawyer for the state said the law as written conflicts with federal regulations on government-issued photo ID. But he said the state has created a new class of photo ID that could be used for a single purpose -- voting.
The court is expected to make a decision quickly.