The U.S. Supreme Court on Sept. 14, 2026, voted 7-2 to uphold a preliminary injunction blocking new U.S. Postal Service rules that imposed unprecedented restrictions on mail voting in federal elections. The ruling leaves the injunction in place as litigation continues and is likely to prevent the rules from affecting the November midterm elections.

State officials and voting rights organizations challenged the rules, arguing that the USPS, an executive agency, lacks authority under the U.S. Constitution to regulate election practices unilaterally. The Supreme Court said in a brief order that the federal government “is unlikely to succeed on the merits of its challenge.” Justices Clarence Thomas and Samuel Alito dissented. The court did not issue a final ruling on the constitutional merits because the case remains pending in federal district court.

How the dispute began

The controversy began in March 2026, when President Donald Trump issued an executive order intended to ensure “integrity in federal elections.” Among other provisions, the order directed the USPS to establish uniform requirements for ballots and envelopes used for mail and absentee voting in federal elections.

The order also required states to provide the Postal Service, 60 days before Election Day, with lists of all voters eligible to vote by mail or absentee. It instructed the USPS not to deliver a mailed ballot if the ballot failed to meet USPS requirements or was submitted by someone not included on a state-provided list, effectively canceling that vote.

Two federal lawsuits were filed immediately, one by state officials and another by voting rights organizations. The plaintiffs argued that the president does not have unilateral authority to change the methods used to conduct federal elections. Under the Elections Clause of the U.S. Constitution, they said, the authority to regulate the “time, place, and manner” of federal elections belongs to the states and, if it chooses to act, Congress.

The cases were assigned to the same federal district court judge in Boston. The judge agreed with the plaintiffs and issued injunctions barring the president and relevant federal officials and agencies, including the USPS, from implementing any part of the executive order concerning mail and absentee voting. The constitutional provision is described in the Elections Clause.

The lawsuit brought by state officials eventually reached the Supreme Court. On Aug. 24, the justices voted 6-3 along ideological lines in favor of the Trump administration. The court did not resolve the constitutional questions. Instead, it held that the states had not shown the injury required to establish standing because the USPS had not yet implemented the executive order and, therefore, had not yet affected the states.

Meanwhile, the USPS began developing the rules and procedures for carrying out the order. The plaintiffs in the voting rights case argued that those steps violated the injunction that remained in effect in their lawsuit. On Aug. 26, however, the district court dissolved that injunction in light of the Supreme Court’s decision in the states’ case. The USPS officially published its new mail-ballot rules that same day. The agency’s federal-election rules were published in the Federal Register.

Rules created confusion for election officials

The USPS rules included three central provisions. First, states had to design ballot envelopes according to USPS specifications and submit the envelopes to the Postal Service for final approval. Second, state and local election officials had to enter voters qualified to vote by mail or absentee into a USPS-operated electronic portal at least 30 days before a federal election. Third, the USPS said that a mailed ballot that did not meet the design requirements, or that was submitted by a person not listed in the electronic portal, “will not be accepted.”

The requirements caused widespread confusion among election officials preparing for the 2026 midterms. The rules did not establish a clear deadline for USPS approval of envelope designs. The portal’s 30-day deadline also conflicted with state voter-registration schedules. Every state permits people to register to vote at some point within the 30 days before Election Day, and many states allow registration even later.

Officials were also left to determine how to comply with the new requirements on short notice. Some states, including North Carolina, had already distributed mail ballots to voters. In Utah, election officials were considering creating their own distribution centers to bypass the USPS rules.

After the rules took effect, the plaintiffs in the two original lawsuits renewed their constitutional challenge, arguing that they now had standing because the USPS had implemented the requirements. On Sept. 4, the federal district court issued a new preliminary injunction pausing implementation and enforcement of the rules. The court found, in essence, that the USPS had likely intruded on the Elections Clause powers of Congress and the states.

On Sept. 6, the federal government asked the Supreme Court to stay, or pause, the preliminary injunction. The government argued that the USPS rules did not improperly interfere with the states’ administration of elections but instead “impose reasonable preparation requirements for certain election-related mail.”

The petition generated 20 amicus briefs, most of them opposing the USPS. One brief was signed by seven Republican chief election officials and described the rules as impractical. The Supreme Court’s Sept. 14 decision upheld the preliminary injunction, with Thomas and Alito dissenting. The court’s statement that the government was “unlikely to succeed on the merits of its challenge” indicated that a supermajority of the justices viewed the USPS as likely to have exceeded its constitutional authority.

The decision does not end the litigation or provide a final determination of the parties’ claims. But with less than two months before Election Day, the preliminary injunction remains in effect with the Supreme Court’s endorsement. As a practical matter, the ruling is likely to settle whether the USPS rules will affect the November midterm elections while the case proceeds in district court. By the time the litigation concludes, the country may already be looking ahead to the 2028 presidential election.

John J. Martin is an assistant professor of law at Quinnipiac University. This article is republished from The Conversation under a Creative Commons license.