The ruling bars the United States Postal Service from implementing restrictions that experts and election officials say would upend voting in November.
The court, which was divided 7-2, with conservative justices Samuel Alito and Clarence Thomas dissenting, upheld a lower court's injunction blocking the United States Postal Service from implementing new rules around who can receive a mail-in ballot ahead of November's vote.
Under this new rule, states would have had to submit lists of eligible voters to the Postal Service, which would then confirm that ballots were sent only to people on that list. The USPS does not typically hold such a role.
"The Government is unlikely to succeed on the merits of its challenge to the District Court's preliminary injunction," Justice Brett Kavanaugh wrote in a concurring opinion with Justice Ketanji Brown Jackson.
Kavanaugh did add, however, that "there is at least a fair prospect that the final rule falls within the Postal Service's statutory authority. But applying the rule in the 2026 elections would be arbitrary and capricious … because state and local election officials do not have sufficient time to reasonably implement the rule before the elections."
Voting by mail has also already begun in some states ahead of November's elections, making the implementation of this plan even more difficult for Americans across the country to vote.
This is a major loss for President Donald Trump, who has long railed against mail-in voting, claiming without evidence that it led to election fraud, and the latest legal defeat the president and his administration have faced in a multipronged approach to undermine trust in US elections .
The White House and the USPS did not respond to a request for comment about the ruling.
"Today, Donald Trump lost another battle in his unconstitutional war to choose his own voters, and the American people are winners," Cisco Aguilar, Nevada's secretary of state, wrote in an emailed statement. "This ruling affirms what our Constitution has always held: Elections belong to the American people, not a desperate man in Washington. Democratic secretaries of state applaud the court on upholding this fundamental principle, and we stand ready to fight any attempt to cause chaos, fear, and intimidation in our elections."
The mail-in voting battle has occurred since the spring, when the president signed an executive order in March titled " Ensuring Citizenship Verification and Integrity in Federal Elections ." The order demanded that all states send the Postal Service a list of voters who would receive mail-in ballots. In turn, the USPS could refuse to deliver ballots to voters not on the lists or ballots that didn't comply with new rules around barcodes and envelopes.
The majority of the provisions of the executive order were quickly blocked by federal courts before the Trump administration appealed the rulings to the Supreme Court in July. Last month, the conservative court ruled along ideological lines to allow the new rules to proceed , writing that the states that sought to block the rules didn't have standing because the rules hadn't been implemented yet.
In the wake of the ruling, a USPS whistleblower claimed that the online portal for the new rules had been hastily thrown together without the necessary care and attention needed for such a critical piece of software.
"The whistleblower's allegations make clear that USPS lacks the technical or operational capability needed to effectively implement the [executive order's] provisions in a way that safeguards every citizen's right to vote in the upcoming midterm elections," Senator Richard Blumenthal, who disclosed the whistleblower's warning, wrote in a letter to the postmaster general. "Despite this, the Trump administration appears intent on USPS moving forward with its flawed plans, no matter the chaos they may create."
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David Gilbert is a reporter at WIRED covering disinformation, online extremism, and how these two online trends impact people's lives across the globe, with a special focus on the 2024 US presidential election. Prior to joining WIRED, he worked at VICE News. He lives in Ireland. ... Read More Reporter Topics government politics elections Donald Trump U.S. Supreme Court Read More The Supreme Court's Mail-In Ballot Ruling Is a Step Toward Chaos in the Midterms The Supreme Court has removed one roadblock from the Trump administration's attempts to impose severe restrictions on voting. David Gilbert ICE Plans to Pay $5 Million to Create National Voting Database As part of a broader DHS surge to investigate alleged voter fraud, ICE has announced it plans to pay up to $5 million to create what amounts to a federal voter database. David Gilbert The County Prosecutors Who Became ICE Informants Illinois prosecutors shared defendants' personal data with federal immigration agents without criminal warrants, public disclosure, or legislative oversight. Aura Bogado A MAGA County's Top Election Official Wants to Hire Election Denial Superstar Tina Peters Tina Peters was convicted of seven counts related to election interference in 2024. Now, she's fielding an offer from a county that's become a hotbed of voting-related conspiracy theories. David Gilbert George Santos Just Got Hit With Kalshi's First-Ever Lifetime Ban The former US representative was also fined more than $71,000 for allegedly attempting to manipulate the prediction market. Kate Knibbs Democrats Have a Plan to Force Trump's Associates to Cooperate With Investigations Donald Trump's West Wing renovations and DC arch could be on the chopping block, should Democrats win the midterms - they could also be leverage. Hugo Lowell Trump Probably Won't Give $5,000 to Every US Adult if Republicans Win the Midterms The eyebrow-raising proposal, delivered during the president's speech at the midterm convention, would cost $1.2 trillion and would need congressional approval. Hugo Lowell You Don't Have a Right to Safe Drinking Water, Trump-Appointed Judge Rules And if your tap water is undrinkable, you have no "constitutional right to truthful information" about it. Sophie Hurwitz Election Officials Are Preparing for Prediction Markets to Sow Chaos in the Midterms From threats to the safety of poll workers to voters who can't distinguish between odds and results, prediction markets are already scrambling the political process. David Gilbert A Judge Has Blocked the Pentagon's Attempt to Blacklist Anthropic A federal judge has called the Department of Defense's designation of Anthropic as a national security supply-chain risk "illegal and baseless." Hugo Lowell A US Census Report on Noncitizen Voting Used Bad Data to Reach Faulty Conclusions Trump has touted a recent Census report. WIRED found grave flaws in its analysis and the process behind it, and confirmed the identity of several of its authors - among them a one-time DOGE affiliate. Vittoria Elliott From Salmonella Eggs to Diarrhea Lettuce, Why This Has Been a Sick Hot American Summer While Trump administration cuts have contributed to the epidemic of foodborne illnesses this summer, there are also deeper issues that make the American food supply chain susceptible to parasites and bacteria outbreaks. Kate Taylor WIRED is obsessed with what comes next. Through rigorous investigations and game-changing reporting, we tell stories that don't just reflect the moment - they help create it. When you look back in 10, 20, even 50 years, WIRED will be the publication that led the story of the present, mapped the people, products, and ideas defining it, and explained how those forces forged the future. WIRED: For Future Reference. More From WIRED
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