The U.S. Supreme Court agreed Monday to review a Mississippi law that allows state election officials to count ballots that arrive up to five days late as long as they're postmarked on or before Election Day, in a case that could impact voting practices nationwide.

The justices granted Mississippi Secretary of State Michael Watson's petition for certiorari challenging the Fifth Circuit's determination that the state's law on late-arriving mail-in ballots was preempted by federal statutes that establish a uniform, nationwide Election Day.

A three-judge panel held in October 2024 that federal statutes governing the election of the president, vice president and members of Congress bar the counting of ballots received after "the Tuesday next after the first Monday in November."

Mississippi is one of 16 states, along with the District of Columbia, that currently allow late-arriving mail-in ballots to be counted as long as they're postmarked by Election Day, according to the National Conference of State Legislatures. Most states require ballots to arrive within 10 days of Election Day, but Washington state has the longest grace period, 21 days.

Watson argued in his June petition for review that while "reasonable people" can argue over whether late-arriving ballots should be counted as a policy matter, there is no dispute that the Constitution leaves that choice up to the states. The defining characteristic of an election is an individual voter's selection of a candidate and submission of the ballot, no matter when state officials receive it, he said.

"As a matter of plain meaning, an 'election' is the conclusive choice of an officer," Watson said. "Voters make that choice by casting — marking and submitting — their ballots by election day. The election has then occurred, even if election officials do not receive all ballots by that day."

Other administrative functions, like the receipt and counting of ballots, can occur and often do occur in the days following Election Day, he added.

Watson said the Supreme Court suggested as much in its 2020 decision in Republican National Committee v. Democratic National Committee, which stayed a federal judge's preliminary injunction that extended the deadline for casting mail-in ballots in Wisconsin's primary election due to the COVID-19 pandemic.

"Extending the date by which ballots may be cast by voters — not just received by the municipal clerks but cast by voters — for an additional six days after the scheduled election day fundamentally alters the nature of the election," the court said in a per curiam emergency docket order.

The Fifth Circuit panel fundamentally misread federal statutes as requiring ballots to be received by state officials by Election Day in order to be valid, Watson said.

The appellate panel, which was composed entirely of appointees of President Donald Trump, pointed to a separate emergency docket ruling issued later in 2020 to support its conclusion that an election is only "consummated" when state officials receive all the ballots, which must occur on Election Day.

In the second emergency docket case, Democratic National Committee v. Wisconsin State Legislature, the Supreme Court declined to implement a Wisconsin federal judge's order extending the state's deadline for voters to return mail-in ballots for the presidential election due to the pandemic. Justice Brett Kavanaugh wrote in a concurrence, "To state the obvious, a state cannot conduct an election without deadlines."

"Congress statutorily designated a singular 'day for the election' of members of Congress and the appointment of presidential electors," the Fifth Circuit panel said in striking down Mississippi's law. "Text, precedent and historical practice confirm this 'day for the election' is the day by which ballots must be both cast by voters and received by state officials."

The Republican National Committee, the Mississippi Republican Party and the Libertarian Party of Mississippi all unsuccessfully opposed Watson's petition for certiorari. Historical election practices prove that the lawmakers who wrote the election statutes intended both the casting and receipt of ballots to be completed on the same day, they argued.

The RNC and state Republican Party chided Watson in an August response brief for asking the court to draw a line that was "unknown" by the drafters of the federal statutes. The receipt of ballots is an essential part of conducting an election, the Republicans said. That was the consensus for the nation's first 100 years and should be the law now.

"The states' unbroken, uniform, decades-long practice of ending ballot receipt on election day is strong evidence that the practice was part and parcel of conducting an 'election,'" they said.

The Libertarian Party added in its own response brief that the fact that Congress established a narrow exception to the receipt deadline for overseas mail-in ballots under various pieces of legislation proves that receipt of ballots by Election Day is the norm.

"The Election Day statutes established the time in which 'the combined actions of voters and officials meant to make a final selection of an officeholder' must occur." the party said. "They necessarily displaced state authority to modify or alter (even slightly) Congress' deadline."

Watson is represented by Scott G. Stewart, Justin L. Matheny and Anthony M. Shults of the Mississippi Attorney General's Office.

The RNC is represented by Gilbert C. Dickey, Thomas R. McCarthy, Cameron T. Norris and Conor D. Woodfin of Consovoy McCarthy PLLC.

The Libertarian Party of Mississippi is represented by T. Russell Nobile, Robert D. Popper and Eric W. Lee of Judicial Watch Inc.

The case is Watson v. Republican National Committee et al., case number 24-1260, in the Supreme Court of the United States.