There will be just one Election Day for this fall's midterm elections — Nov. 3. But voters in 14 states who cast their votes by mail have been given a grace period ranging from a day later to several weeks in which their ballots can be received and counted.

Whether that extra time should be allowed is at the heart of a case that will be argued Monday before the U.S. Supreme Court. If the court strikes down those grace periods, it will leave those states — and their voters — scrambling to adjust with only a few months before absentee ballots are sent out for this fall's midterm elections.

The implications could extend well beyond the 14 states that give a grace period for regular ballots, depending on how the court ultimately rules. A total of 29 states allow extra time for at least some mail voters, including those who cast military and overseas ballots, according to the National Conference of State Legislatures and the Voting Rights Lab.

In a filing with the court, a group of state and big-city election officials cited “the risks of confusion and disenfranchisement” if mail ballot grace periods were ended suddenly in states where voters have counted on them for years.

Stuart Holmes, director of elections for the Washington Secretary of State’s office, said 127,000 ballots were received after Election Day in 2024, so voters should expect about that many ballots to be rejected if Mississippi loses the case. Washington has the longest grace period of any state, 21 days after Election Day.

If the ruling is that a ballot is invalid even if it's postmarked by Election Day, “it might as well have never been received,” he said.

“There’s no way to resolve that issue," Holmes said. "There’s no second chance.”

The practice of counting ballots after Election Day has been a target of President Donald Trump since he sought to “STOP THE COUNT” after the 2020 election. He and his allies argue it delays results and leads to suspicions about the vote tallies. It's part of Trump's broader attack on most mail balloting, which he has said breeds fraud despite findings to the contrary and years of experience in numerous states.

The Republican National Committee and the Libertarian Party of Mississippi brought the lawsuit against Mississippi Secretary of State Michael Watson, a Republican, arguing that federal Election Day statutes envision a single day for casting ballots. Grace periods for receiving mail ballots — also in place in the District of Columbia and three U.S. territories — violate federal law, they argue.

“Election Day is Election Day for a reason,” Ohio state Sen. Theresa Gavarone, a Republican, said during debate over her state's ban on the practice last year. “Allowing ballots to be delivered days after the election does nothing but hurt the integrity and credibility of our elections.”