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.