A handful of other states also use voters' inactivity to trigger a process that could lead to their removal from the voting rolls.
In the 5-4 decision (pdf), the court found that the state, which drops people from the rolls if they don't vote and then don't respond to notices to confirm their residency, does not violate the National Voter Registration Act (NVRA).
"Ohio's process cannot be unreasonable because it uses the change-of-residence evidence that Congress said it could: the failure to send back a notice coupled with the failure to vote for the requisite period", Supreme Court Justice Samuel Alito write in the decision.
Justice Samuel Alito says that OH is complying with the 1993 National Voter Registration Act.
Justice Stephen Breyer issued a dissenting opinion, which Justice Ruth Bader Ginsburg, Sonia Sotomayor and Elena Kagan - the other members on the court's liberal wing - joined. More than half the voters in OH fail to cast a ballot over a two-year period, the group said, and those who receive the state's notices simply throw them away.
The ruling could be a major victory for Republicans, who tend to benefit from lower voter turnout, and a stinging loss for Democrats, who do best in high-turnout elections.
5-4 SCOTUS Ruling Threatens Voting Rights, Affirms Ohio Voter Purge Rule Which Discourages Minority Turnout
Partisan fights over ballot access are being fought across the country. "In my view, Ohio's program does just that".
OH said it only uses the process after first comparing its voter lists with U.S. Postal Service lists of changed addresses, but not everyone who moves notifies the post office.
The state argued that the policy was needed to keep voting rolls current, clearing out people who have moved away or died. "The only question before us", Alito made clear, is whether the practice "violates federal law". Indeed, the majority stressed, not only "are States allowed to remove registrants who satisfy these requirements, but federal law makes this removal mandatory". As part of the lawsuit, a judge past year ordered the state to count 7,515 ballots cast by people whose names had been removed from the voter rolls.
"Communities that are disproportionately affected by unnecessarily harsh registration laws should not tolerate efforts to marginalize their influence in the political process, nor should allies who recognize blatant unfairness stand idly by", added Sotomayor, the first Hispanic Supreme Court justice.
After the last presidential election, the department switched sides in the case, Husted v. A. Philip Randolph Institute, No. 16-980. A three-judge panel on that court had ruled 2-1 that Ohio's practice was illegal.More news: Robbie Keane raves about Tottenham Hotspur striker Harry Kane