More: Writing for the 5-4 majority, Barrett said the federal law doesn't set a deadline for ballots to received so Mississippi's law doesn't conflict with federal rules.

"The question today is not whether requiring ballots to be received by election day is a good or bad idea; the question is whether the idea has made its way into the United States Code," she wrote.

More than a dozen states have similar laws. Additional states allow late-arriving ballots from military and overseas voters. Voting by mail has decreased since its peak during the COVID-19 pandemic. But nearly 30% of voters still cast a ballot that way in the 2024 elections.