The U.S. Supreme Court declined on Tuesday to hear a bid by civil and voting rights groups to end Pennsylvania's mandate that mail-in ballots bear a handwritten date on the outer envelope, a requirement they contend is unnecessary and has resulted in needless disqualification of legitimate ballots.

The Supreme Court said Tuesday it won’t hear civil rights groups’ appeal seeking to invalidate Pennsylvania’s dating requirement for mail ballots, which has invalidated thousands of votes each recent election and become a central legal fight over voting in the key swing state.

The Pennsylvania Supreme Court said Friday it will again consider whether voters should have to write the correct date on return envelopes for mail ballots to be counted.

The Supreme Court will now decide whether the Pennsylvania Commonwealth Court made the right decision in November when it ruled Philadelphia had violated voters rights by rejecting undated ballots in its special election. That ruling, which came days before the November election, was blocked from taking effect in the critical election.

Justices said Friday they will decide whether the dating rule for absentee and mail ballot return envelopes violates a state constitutional provision that elections must be free and equal.