A Supreme Court ruling allows the Trump administration to move ahead with plans to restrict mail ballots, potentially affecting the nation's heavy reliance on voting by mail. Nearly one in three voters used this method in recent elections, a practice that peaked during the Covid pandemic when over 40 percent of voters used mail ballots in 2020. The use of mail voting varies significantly by state, depending on local rules.

Several states with the highest rates oppose the restrictions, forming a coalition of nearly two dozen states, mostly run by Democrats, that sued to block the efforts. In March, Mr. Trump put forward an executive order to overhaul voting and instructed the Department of Homeland Security to develop state-by-state lists of citizens to determine voting eligibility. He also directed the Postal Service to help decide which voters should receive mail-in ballots.

The Postal Service published regulations related to the order, requiring states to share voter data with the federal government and setting new requirements for mail ballot envelopes. It remains unclear if the plans will apply to the November midterm elections, as a lower court is still determining their legality. States have little time to prepare for procedural changes, with many set to begin sending out mail ballots in just a few weeks.

Christine Zhang contributed reporting.