The U.S. Postal Service’s proposed rule to tighten mail-in voting procedures could significantly restrict voting by mail for millions of Americans ahead of the November midterm elections, with potential implications for key battleground states. The rule, which has been temporarily blocked by a federal judge following multiple lawsuits, would require states to provide detailed voter data and implement new mailing processes. The administration is appealing the ruling as the November elections approach.

The rule would specifically impact voters in states where mail voting is widespread or universal, such as Michigan and California, as well as rural and older voters who often rely on mail ballots. Democratic voters tend to use mail voting more than Republicans, increasing the likelihood that any restrictions would disproportionately affect Democratic turnout.

Michigan, with nearly 2 million voters on a permanent mail voting list and a slew of competitive races including a crucial Senate contest and closely contested gubernatorial and legislative battles, stands out as a key state under the new rule. Analysis by the M.I.T. Election Data and Science Lab shows that Democrats in Michigan cast a significantly higher proportion of their votes by mail than Republicans—60 percent vs. 34 percent in 2024, a gap that has widened amid heightened partisan rhetoric on mail voting.

The rule would require states to upload voter information to a federal portal, which is not yet operational, raising logistical hurdles that election officials say may not be surmountable within the limited time before Election Day. Nearly two dozen Democratic-led states and Washington, D.C., have sued to block the rule, signaling resistance to the measure and reluctance to share voter data with federal authorities. The administration states the voter data is necessary to identify noncitizens who may be registered to vote, a claim disputed by opponents who view the rule as a tactic aimed at discouraging mail voting among Democratic supporters.

Election administrators warn the rule would complicate election logistics nationwide, potentially forcing small jurisdictions to acquire new technology and reroute ballots through major mail sorting centers that can handle barcodes required under the rule. Officials from both parties have cautioned that such rapid changes could introduce confusion and delays, particularly in rural areas where resources are limited.

States that send mail ballots to all voters, including Washington and Arizona, could see substantial disruption. In Arizona, where about 80 percent of voters cast ballots by mail in 2022, Secretary of State Adrian Fontes expressed concern that restricting mail voting could provoke backlash among Republican voters who heavily use mail ballots, potentially altering the state's political dynamics.

Republican officials have offered differing perspectives. Michigan state Senator Jim Runestad said he was unaware of any plans to adjust campaign strategies in response to the rule and emphasized the need to safeguard election integrity. He noted increasing mail voting within the Republican base but suggested a preference for in-person voting on Election Day.

Legal challenges to the Postal Service rule remain unresolved. The Supreme Court recently declined to rule on the issue, citing prematurity, but justices may revisit the question now that the rule is finalized and lower courts have intervened. Meanwhile, election officials and voting rights advocates across the country continue to assess the possible impact of last-minute regulatory changes on the administration of mail-in voting in the upcoming midterms.