The justices overruled a federal appeals court that had ordered Ohio's top elections official to do more to help counties verify voter eligibility.
Secretary of State Jennifer Brunner, a Democrat, faced a deadline of Friday to set up a system to provide local officials with names of newly registered voters whose driver's license numbers or Social Security numbers on voter registration forms don't match records in other government databases.
Ohio Republicans contended the information for counties would help prevent fraud. Brunner said the GOP is trying to disenfranchise voters.
In a brief unsigned opinion, the justices said they were not commenting on whether Ohio is complying with a provision of the Help America Vote Act of 2002 that lays out requirements for verifying voter eligibility.
Instead, they said they were granting Brunner's request because it appears that the law does not allow private entities, like the Ohio GOP, to file suit to enforce the provision of the law at issue.
"They didn't deal with the merits of the case," said Ohio GOP Chairman Bob Bennett. "What they dealt with was a technicality on whether we had standing or not to bring the action."
About 200,000 of 666,000 voters who have registered in Ohio since Jan. 1 have records that don't match. Brunner has said the discrepancies most likely stem from innocent clerical errors rather than fraud but has set up a verification plan.
Bennett said Brunner could have set up a system months ago to check the discrepancies and that her actions have left the potential for voter fraud.
"If we have a close election in Ohio and there's any doubts, the failures will be laid right at her doorstep," Bennett said.
Brunner said the court's decision would help ease confusion in the run-up to Election Day.
She said the act was clear that the mismatch lists were to be used to maintain the voter database, not to determine voter eligibility.
"We are very pleased that the court recognized that this was an illegal challenge on the part of the Republicans," she said.
She said the office would have found a way to comply, but there were risks that qualified voters would have been disqualified.
"I think it's an unfair tactic to subject voters to this kind of uncertainty and anxiety this close to such an important election," she said.
In court filings, the GOP has not produced any specific evidence of voting fraud, only unsubstantiated reports that voters from other states had cast fraudulent ballots during the early voting period.
McCain campaign manager Rick Davis said lower court rulings have clearly said regulations issued under the act require the secretary of state to match against the list, find where there's been fraud and inconsistencies and report them to counties.
"Why in the world would that not happen? We have the technology, the budget, the means and the manpower to make that happen," Davis told reporters on a conference call.