Mail-in ballots in Pennsylvania with incorrect dates will not be counted, as ruled by the court.

In the 2020 presidential election, where 19 electoral college votes are at stake, the Pennsylvania Supreme Court ruled that mail-in ballots without the correct dates on envelopes cannot be counted.

The state's high court ruled that a lower court that found the mandate unenforceable should not have taken up the case because it did not involve all 67 election boards, as only two left-leaning groups sued Philadelphia and Allegheny counties.

The Pennsylvania Supreme Court ruled that the Commonwealth Court did not have the authority to review the matter, as stated in a court document.

The Commonwealth Court has ruled that mail-in ballots must be properly dated in order to be counted, effective immediately.

The ruling was hailed by Republicans as a triumph for voter authenticity in the fiercely contested state, while voting rights activists, including the American Civil Liberties Union, vowed to explore further legal avenues.

In 2020, President Joe Biden won the state of Pennsylvania by more than 80,000 votes, and this week, former President Trump and Vice-President Harris have been campaigning in the Keystone State.

Nearly 16,000 mail-in ballots were disqualified for irregularities in the April primary election, with about half of them being rejected due to issues such as missing signatures and incorrect dates on outer envelopes. The New York Times reports that almost 75% of the mail-in ballots requested were made by Democrats.

In 2020, approximately 2.5 million Pennsylvanians cast their ballots through mail, as stated in a lawsuit filed by Republicans following the election, which aimed to challenge the constitutionality of universal mail-in voting.

Michael Whatley, RNC Chairman, declared the Friday ruling a "huge" victory for election integrity.

"The PA Supreme Court REJECTED a Democrat attempt to count undated ballots following legal action from the RNC and @PAGOP, making mail voting in the Keystone State less susceptible to fraud. We will keep fighting and winning!"

The ruling was a setback for Pennsylvania voters, according to Steve Loney, the senior supervising attorney for the ACLU in Pennsylvania.

"Loney stated that eligible voters who submitted their ballots on time should have their votes counted and their voices heard. He emphasized that the right to vote is a fundamental right that Pennsylvanians cherish, and it should not be taken away due to a minor paperwork mistake."

The Supreme Court vacated the Commonwealth Court decision with a 4-3 ruling, as two Democrats joined both Republicans in the decision.

The three Democratic justices disagreed with the majority decision and believed the high court should have heard the dispute.

Justice David Wecht wrote that a prompt and definitive ruling on the constitutional question presented in the appeal is crucial because it will affect the counting of ballots in the upcoming general election. He and the two other dissenters would have ruled on the matter based on written briefs.

In the 2020 election, Republicans attempted to exclude mail-in ballots received after election day from being counted, but the Supreme Court upheld the Pennsylvania Supreme court's decision to count these ballots if they were received within three days of election day, regardless of the postmark's legibility.

The Associated Press and Reuters contributed to this report.