WASHINGTON, D.C. – The U.S. Supreme Court is hearing arguments in a consequential case Monday morning to determine whether mail-in ballots must be received by Election Day.

The case, Watson v. Republican National Committee, centers around a Mississippi law that allows mail-in ballots to be counted up to five days after an election as long as they are postmarked by Election Day. The Mississippi law was enacted in 2020 due to the COVID-19 pandemic.

Thirteen other states have similar laws that allow domestic mail-in ballots to be received after Election Day, as long as the ballot is postmarked by the date of an election. In Illinois, mail-in ballots can be received up to 14 days after an election.

Lawyers for the Republican National Committee argued that federal law sets the Tuesday after the first Monday in November as Election Day.

Nineteen states and the District of Columbia filed a brief to the U.S. Supreme Court that argued states should have the ability to set rules over the receipt of ballots. The states said mail-in ballot deadlines give voters an opportunity to cast their ballots.

“States have the constitutional authority to make individualized judgments on how best to receive and count votes in federal elections,” representatives for the states wrote.

The states argued overseas military ballots could be affected by a ruling in the case. However, election advocates said Congress’ passage of the Uniformed and Overseas Citizen Voting Act established requirements for states to send absentee ballots 45 days before a federal election.

The case will be argued throughout the morning and a decision is expected by July.