Pennsylvania’s Republican legislative leaders asked the U.S. Supreme Court on Monday to stop a decision by the state’s high court to count mail-in ballots received up to three days after Election Day.

The Pennsylvania Supreme Court ruled in Democrats’ favor on a number of mail-voting rules: permitting voters to turn in ballots via drop box in addition to using the U.S. Postal Service; allowing ballots to be returned up to three days after Election Day; and blocking a Republican effort to allow partisan poll watchers to be stationed in counties where they do not live.

The legislators asked the U.S. Supreme Court to weigh in only on the ruling pushing back the deadline for mail ballots to arrive. The state court said such ballots must be counted if they are postmarked by Nov. 3 — and even if they are not, “unless a preponderance of the evidence” shows that the ballots were mailed after Election Day. The state Republican Party later filed a similar stay request.

It is one of many legal battles being waged across the country regarding voting rules in advance of the Nov. 3 election. But Pennsylvania has particular significance because it is crucial to President Trump’s reelection fortunes. He defeated Hillary Clinton there in 2016 by 44,000 votes, or less than 1 percent.

“In a year where there is a very real possibility that the final presidential election result hinges on Pennsylvania, the new rules imposed by the decision of the Supreme Court of Pennsylvania (a body elected in partisan elections) could destroy the American public’s confidence in the electoral system as a whole,” said the stay request filed by the Republican leaders.

The request was filed with Justice Samuel A. Alito Jr., who oversees the U.S. Court of Appeals for the 3rd Circuit in Philadelphia. It is likely to be referred by him to the entire court.

The justices usually are reluctant to intervene in legal battles over voting close to an election. The court often defers to state courts over such matters.

It is the first election-related case to be filed with the court since the death of Justice Ruth Bader Ginsburg. She wrote a biting dissent in April, when the court voted 5 to 4 to stop some of the accommodations federal judges had allowed for Wisconsin primary voters because of the pandemic.

“The concerns advanced by the court and the applicants pale in comparison to the risk that tens of thousands of voters will be disenfranchised,” she wrote for her liberal colleagues. “Ensuring an opportunity for the people of Wisconsin to exercise their votes should be our paramount concern.”

Even in that case, though, the conservative majority allowed Wisconsin officials to count ballots received after the day of the primary if it was clear they had been mailed by then.

Pennsylvania lawmakers said the decision of its state court extends Election Day beyond what is called for in the Constitution and takes away the power of legislatures to set election rules. The changes are tied to challenges of the pandemic, they said, but “the Supreme Court of Pennsylvania’s own special master found that COVID-19 is not likely to disrupt the November General Election ballot receipt deadline.”

The U.S. Supreme Court is likely to call for a response from the Democrats who filed suit in Pennsylvania before acting on the request.

Amy Gardner contributed to this report.