A requirement for Pennsylvania voters to put accurate handwritten dates on the outside envelopes of their mail-in ballots does not run afoul of a civil rights law, a federal appeals court panel said Wednesday, overturning a lower court ruling.

A divided 3rd U.S. Circuit Court of Appeals ruled to uphold enforcement of the required date on return envelopes, a technical mandate that caused thousands of votes to be declared invalid in the 2022 election.

The total number is a small fraction of the large state’s electorate, but the court’s ruling puts additional attention on Pennsylvania’s election procedures ahead of a presidential election in which its Electoral College votes are up for grabs.

A lower court judge had ruled in November that even without the proper dates, mail-in ballots should be counted if they are received in time. U.S. District Judge Susan Paradise Baxter said the envelope date is irrelevant in helping elections officials decide whether a ballot was received in time or if a voter is qualified.

In the court’s opinion, Judge Thomas Ambro said the section of the 1964 Civil Rights Act that the lower court relied upon does not pertain to ballot-casting rules broadly, such as dates on envelopes, but “is concerned only with the process of determining a voter’s eligibility to cast a ballot.”

“The Pennsylvania General Assembly has decided that mail-in voters must date the declaration on the return envelope of their ballot to make their vote effective,” Ambro wrote. “The Supreme Court of Pennsylvania unanimously held this ballot-casting rule is mandatory; thus, failure to comply renders a ballot invalid under Pennsylvania law.”

The American Civil Liberties Union of Pennsylvania, which helped represent groups and voters who challenged the date mandate, said the ruling could mean thousands of votes won’t be counted over what it called a meaningless error.

“We strongly disagree with the panel majority’s conclusion that voters may be disenfranchised for a minor paperwork error like forgetting to write an irrelevant date on the return envelope of their mail ballot,” Ari Savitzky, a lawyer with the ACLU’s Voting Rights Project who argued the appeal, said in a statement. “We are considering all of our options at this time.”

State and national Republican groups defended the date requirement, and the Republican National Committee called the decision a “crucial victory for election integrity and voter confidence.”

In Pennsylvania, Democrats have been far more likely to vote by mail than Republicans under an expansion of mail-in ballots enacted in 2019.