The US supreme court has rejected Donald Trump’s attempt to restrict mail-in ballots ahead of November’s midterm elections in a major blow to the president.

In a one-paragraph decision that did not explain the court’s reasoning, the justices on Monday left in place a lower court’s ruling that blocked Trump’s executive order requiring the US Postal Service (USPS) to curtail voting by mail.

“The Government is unlikely to succeed on the merits of its challenge to the District Court’s preliminary injunction,” the justices wrote in the unsigned decision. “And the equitable factors applicable for obtaining emergency relief from this Court do not favour a stay.”

Justices Samuel Alito and Clarence Thomas dissented.

Justice Brett Kavanaugh, writing in a concurrence, said applying limits to mail-in ballots ahead of the midterms “would be arbitrary and capricious in violation of the Administrative Procedure Act because state and local election officials do not have sufficient time to reasonably implement the rule before the elections”.

The decision thwarts Trump’s attempt to overhaul the electoral system, which he has repeatedly pledged to do while continuing to push unfounded claims of widespread fraud in the 2020 presidential election.

However, Kavanaugh’s focus on how Trump’s order failed to give election officials enough time to adapt before November leaves open the possibility that curbs on mail-in ballots could still be implemented ahead of the 2028 presidential race.

Kavanaugh said there was “at least a fair prospect” that it would fall within the US Postal Service’s authority to implement new rules on mail-in ballots.

Mail-in ballots have long been in Trump’s crosshairs, as they are more popular among Democratic voters compared with Republicans. Overall, about one-third of voters vote by mail.

The supreme court decision follows months of legal wrangling on mail-in voting. The president in March issued an executive order mandating the creation of a federal list of eligible voters and directed the postal service to limit mail ballot deliveries to those people.

Solicitor-general John Sauer had argued to the top court that the postal service’s final rule required “only modest envelope-design and addressee-information requirements” for ballots sent by mail. It ensures states carry the responsibility for determining voter eligibility but does not dictate ballot content, counting procedures or deadlines, he said.

“The rule thus plainly does not seize control of states’ administration of elections – it simply imposes reasonable preparation requirements for certain election-related mail,” Sauer said.

Attorneys for the 23 states that sued to block the order said there’s “nothing ‘modest’, equitable or lawful” about the new restrictions. It would take “Herculean” efforts by state and local election officials to even begin to comply, they said.

“In some states, unrebutted evidence establishes that compliance with USPS’s rule would be impossible ahead of the midterms, meaning that millions of voters would be unable to vote by mail and some would not be able to vote at all,” the states’ attorneys said, noting that areas including North Carolina and Wisconsin had started mailing ballots.

In his dissent, Alito took issue with the states’ argument that they lacked the time to comply with the new rules, saying they “cannot claim the timing of the rule tilts the equities in their favour when they, and the courts hearing their claims, are responsible for so much of the delay.”

Lawyers for voting rights groups that sued said the restrictions were “unprecedented eleventh-hour requirements”, asserting no federal statute nor the constitution assign the executive branch such power.

California senator Alex Padilla, the Democratic ranking member of the committee on rules and administration, celebrated the decision on Monday evening.

“Trump tried to rewrite the rules. He lost. We won. Vote by mail works. California, ballots start going out to every registered voter in October. Go make your voice heard,” he wrote on X.

The supreme court previously ruled that an initial legal challenge to Trump’s executive order was premature, allowing it to take temporary effect without pronouncing on its legality.

The ruling followed a federal judge’s decision to indefinitely freeze the postal service plan as challenges to it moved through the courts.

A federal appeals court last week kept that block in place, saying that allowing the rule change would be likely to “result in the disenfranchisement of millions of voters across the country while providing minimal – if any – gains in combating voter fraud”. – Copyright The Financial Times Limited 2026