HARRISBURG — 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 have been thrown out 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 68-page 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.

Enforcement of the dating provision resulted in at least 10,000 ballots getting thrown out in the 2022 midterm election alone, the lawsuit said.

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 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 Trump baselessly claiming that mail-in voting is rife with fraud.

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.