The law provides that those who cannot show the proper form of identification at the polls may cast provisional ballots, and would then have six days have to produce a voter ID or their votes would not be counted, The Philadelphia Inquirer reported.
The high court voted 4-2 to return the issue to the lower court, and said if the lower court holds the law is being implemented in such as way as to ensure all voters have access to the required photo ID, the law can stand, but if not, the law would be overturned.
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 this year that the stringent voter ID law would allow Republican nominee Mitt Romney to carry the state.
Opponents of the law asked the high court to grant an injunction that would keep the law from being implemented for the November election.
David Gersch, representing the challengers, told the court Pennsylvania has not allowed enough time to ensure all voters who require it get photo ID, and said the law's backers have produced no instance of in-person voter fraud.
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.