HARRISBURG, Pa. (AP) — 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.