The U.S. Supreme Court announced on Monday that it will hear a case challenging Illinois’ law permitting mail-in ballots to be counted up to 14 days after Election Day, provided they are postmarked or certified by voters on or before Election Day. The case, brought by Republican Congressman Mike Bost of southern Illinois and two presidential elector nominees, contests the state’s policy as conflicting with federal statutes that set a uniform Election Day for federal elections.

Bost and the other plaintiffs filed suit in 2022 against the Illinois State Board of Elections, arguing that the state’s extended ballot receipt window violates federal law and the U.S. Constitution. They claim that counting ballots after Election Day dilutes the impact of timely votes and imposes additional burdens on candidates, such as requiring extended campaign monitoring and increased costs.

Illinois is among roughly 20 states that accept and count mail-in ballots received after Election Day, as long as they are postmarked by that date. The law has been defended as a means to ensure that all eligible votes, including those from military personnel and overseas voters, are counted.

The case was dismissed by both a federal district court and the U.S. Court of Appeals for the Seventh Circuit. Both courts found that Bost and the electors lacked legal standing, meaning they could not show they were directly harmed by the law. The appellate court’s majority held that the harm alleged by Bost, such as additional campaign expenditures and potential vote dilution, was too speculative. A dissenting judge argued that, as an active candidate, Bost should be considered more than a bystander and that the financial and strategic burdens imposed by the law were real and particularized.

The Supreme Court’s review is narrowly focused on the procedural question of standing—whether Bost and the other plaintiffs have sufficiently demonstrated a direct, concrete injury that would allow them to challenge the law in federal court. The justices are not expected to address the underlying merits of whether Illinois’ law violates federal election statutes at this stage.

If the Supreme Court rules that Bost has standing, the case could be sent back to the lower courts for further proceedings on the substantive legal questions.

The challenge comes amid ongoing Republican efforts, led by allies of former President Donald Trump, to restrict the counting of mail-in ballots received after Election Day. These efforts intensified following the 2020 election, which saw a surge in mail-in voting due to the COVID-19 pandemic.

The Supreme Court will likely hear oral arguments in the case this fall, with a decision expected by June 2026.