The GOP has asked the Supreme Court to review a Pennsylvania ruling that extends the mail-in voting deadline for the presidential election, a move that could lead to the court’s first test since the death of Justice Ruth Bader Ginsburg, law experts say.

Pennsylvania's Supreme Court ruled last week that there will be a three-day extension for mail-in ballots as long as they're postmarked by 8 p.m. on Nov. 3, Election Day. Previously, ballots were due when the polls close on Election Day, but the state's Democratic Party filed a lawsuit to push back the deadline. Republicans have argued that expanding mail-in voting could give Democrats an unfair edge in the election.

The Pennsylvania court wrote that ballots "received within this period that lack a postmark or other proof of mailing, or for which the postmark or other proof of mailing is illegible, will be presumed to have been mailed by Election Day unless a preponderance of the evidence demonstrates that it was mailed after Election Day."

On Tuesday morning, Republicans filed a petition for the Supreme Court to review the ruling, arguing that the decision violates federal law that mandates "holding all elections for Congress and the Presidency on a single day throughout the Union."

Ginsburg, a member of the Supreme Court's liberal wing, died on Friday at the age of 87. Her death leaves the court with a 5-3 conservative majority and gives President Donald Trump the opportunity to further shape the highest court in the nation.

"This could be a big first test for the post-RBG Supreme Court and where it will stand on election issues," said Rick Hasen, election law expert and law professor at the University of California Irvine, according to The Hill. "There's little reason to believe that the conservative-liberal divide will disappear with Justice Ginsburg's death."

The Pennsylvania case is one of hundreds filed regarding election laws and the Supreme Court's conservative majority following Ginsburg's death could shape how voting rights cases are decided ahead of the election, Forbes reported. Other lawsuits have been filed in other pivotal swing states including Wisconsin, Michigan, and Georgia, according to the publication.

Trump has said mail-in voting would make the election "rigged" and "fraudulent," while saying voting by mail is secure in Florida _ a crucial swing state _ because "we defeated Democrats' attempts at change." He also said the state has "a great Republican governor" while explaining his support for mail-in voting in Florida.

Studies have found that mail-in voting does not benefit one party more than the other, FiveThirtyEight reported.

An Axios/Ipsos poll found Democrats are more likely to be concerned about in-person voting as a risk for getting COVID-19. Fifty-two% of respondents said in-person voting was risky. Sixty-four% of Democrats said it was risky compared to 29% of Republicans. The poll was conducted July 31-Aug. 3 with a margin of error of 3 to 3.4 percentage points.

Another poll from Yahoo News/YouGov _ with a margin of error of plus or minus 3.3 percentage points _ found 55% of Trump supporters said they won't view Democratic presidential candidate Joe Biden's win as legitimate if mail-in voting puts him over Trump.

There’s evidence of a large partisan gap over which method people intend to use to vote. Of those who said they would rather vote in person, Trump leads Biden 59% to 28% _ while Biden leads Trump 70% to 14% among respondents who said they would prefer to vote through mail, according to the Yahoo News/YouGov poll.