Pennsylvania's Supreme Court ruled in favor of the Democratic Party's request to extend the deadline for mail-in votes to three days after the 2020 US election.
The court ruled 5-2 in favor of the Democrats, according to the Associated Press.
In order for ballots to be eligible, they must be postmarked by the time the polls close and be received by the county board of election by 5pm on 6 Nov, three days after Election Day.
Republicans opposed extending the deadline.
There are 18 states - half of which have Republican governments - with post-Election Day deadlines.
In addition to the deadline change, the Supreme Court also voted in favor of state Democrats by allowing them to fix errors and "gray areas" of the state's mail-in voting laws, by kicking the Green Party's candidate off the November ballots and by approving the use of satellite election offices and county drop boxes for ballots.
Satellite election offices are especially important in densely populated - and often more Democratic leaning - areas of the state, like Philadelphia.
The satellite locations will help elections officials manage the expected tide of mail-in ballots by providing alternative in-person voting locations.
A 2019 state law expanded mail-in balloting in Pennsylvania, and - due to the pandemic - state elections officials are expecting more than 3 million voters to vote by mail this year.
Despite the general Republican preference for in-person voting - ostensibly to avoid voter fraud, despite numerous experts claiming that threat is minimal - Pennsylvania Republicans opposed authorizing the satellite locations, which makes voting in-person more viable.
They complained that the use of offices or drop boxes was not explicitly authorized under state law.
Green Party candidate Howie Hawkins ultimately was removed from the November ballot after the Supreme Court reversed a lower court's decision to include him.
Democrats - who historically have worked to keep the Green Party off the ballot over fears they will split the liberal vote - argued this year that there were irregularities in the way the Green Party filed its affidavits related to the 5,000 name petition candidates must collect in order to get their names on the ballot.
