PENNSYLVANIA – A new lawsuit filed Tuesday by a constellation of left-leaning groups in Pennsylvania is trying to prevent thousands of mail-in ballots from being thrown out in November’s election in a battleground state that is expected to play a critical role in selecting a new president.

The lawsuit, filed in a state court, is the latest of perhaps a half-dozen cases to challenge a provision in Pennsylvania law that voters must write the date when they sign their mail-in ballot envelope.

Voters not understanding that provision has meant that tens of thousands of ballots lacked an accurate date since Pennsylvania dramatically expanded mail-in voting in a 2019 law.

The latest lawsuit says multiple courts have found that a voter-written date is meaningless in determining whether the ballot arrived on time or whether the voter is eligible. As a result, rejecting someone’s ballot either because it lacks a date or a correct date should violate the Pennsylvania Constitution’s free and equal elections clause, the lawsuit said.

“This lawsuit is the only one that is squarely addressing the constitutionality of disenfranchising voters under Pennsylvania’s Constitution,” said Marian Schneider, a lawyer in the case and senior policy counsel for voting rights for the American Civil Liberties Union of Pennsylvania.

In the lawsuit, the plaintiffs’ lawyers — including the ACLU, the Public Interest Law Center and the Arnold & Porter Kaye Scholer law firm — referenced a 2023 opinion in which state Supreme Court justices seemed to invite such a challenge. In it, they suggested that the free and equal elections clause would indeed prevent ballots from being thrown out for failing to comply with the date requirement.

Enforcement of the dating provision resulted in at least 10,000 ballots getting thrown out in the 2022 mid-term election alone, the lawsuit said. Lawyers in the case said research shows that a disproportionate share of rejected ballots come from older voters, poorer districts and Black and Latino communities.

The lawsuit names Democratic Gov. Josh Shapiro’s top election official, as well as the election boards in Philadelphia and Allegheny County, both heavily Democratic jurisdictions.

However, Democrats have fought repeatedly to undo the dating requirement, while Republicans in the past have fought in court to ensure that counties can and do throw out mail-in ballots that lack a complete or correct date.

Roughly three-fourths of mail-in ballots tend to be cast by Democrats in Pennsylvania, possibly the result of former President Donald Trumpbaselessly claiming that mail-in voting is rife with fraud.

Shapiro’s Department of State did not comment on the lawsuit. But it said in a statement that it is “irrefutably clear that the handwritten date serves no function in the administration of Pennsylvania’s election” and that it has consistently argued in court that voters shouldn’t have ballots rejected for incorrectly writing it.

A November ballot in Pennsylvania that likely will feature President Joe Biden and Trump at the top of the ticket also will feature a high-profile Senate contest between Democratic Sen. Bob Casey and Republican challenger David McCormick.

Republicans are urging their voters to cast ballots by mail. Still, national Republican groups signaled that they will oppose the lawsuit.

The National Republican Senatorial Committee accused Democrats of attempting to “change the rules at the last minute in a desperate bid to hold onto power.” The Republican National Committee claimed the date requirement is an “important election integrity safeguard” and that lawsuits like the one filed Tuesday “are designed to undermine voter confidence and make mail voting less secure.”

The plaintiffs in the lawsuit include the Black Political Empowerment Project, POWER Interfaith, Make the Road Pennsylvania, OnePA Activists United, New PA Project Education Fund, Casa San José, Pittsburgh United, League of Women Voters of Pennsylvania and Common Cause Pennsylvania.

Currently, a separate challenge to the date requirement is pending in federal court over whether it violates the 1964 Civil Rights Act or the Constitution’s equal protection clause. In March, a divided 3rd U.S. Circuit Court of Appeals ruled that the date requirement does not violate the civil rights law.