US president-elect Joe Biden and vice president-elect Kamala Harris hold a press conference on November 19 in Wilmington, Delaware. Photo: AFP

The US Supreme Court on Tuesday handed a defeat to Republicans seeking to throw out up to 2.5 million mail-in ballots in Pennsylvania as they try to undo President Donald Trump's election loss, with the justices refusing to block the state from formalizing President-elect Joe Biden's victory there.

The court in a brief order rejected a request by US congressman Mike Kelly, a Trump ally, and other Pennsylvania Republicans who filed a lawsuit after the November 3 election arguing that the state's 2019 expansion of mail-in voting was illegal under state law.

Pennsylvania was one of the pivotal states in the election, with Biden, a Democrat, defeating Trump after the Republican president won the state in 2016. State officials had already certified the election results.

There were no noted dissents from any of the justices on the court, which has a 6-3 conservative majority including three Trump appointees. Trump had urged the Republican-led Senate to confirm his most recent nominee, Justice Amy Coney Barrett, before Election Day so she could participate in any election-related cases.

Trump has falsely claimed that he won reelection, making unfounded claims about widespread voting fraud in states including Pennsylvania. Democrats and other critics have accused Trump of aiming to reduce public confidence in the integrity of US elections and undermine democracy by trying to subvert the will of the voters.

"This election is over. We must continue to stop this circus of 'lawsuits' and move forward," Pennsylvania Attorney General Josh Shapiro, a Democrat, wrote on Twitter.

The Supreme Court also must decide what to do with another election-related case brought on Tuesday. 

Republican-governed Texas, hoping to help Trump, mounted an unusual effort to overturn the election results in Pennsylvania and three other states - Georgia, Michigan and Wisconsin - by filing a lawsuit against them directly at the Supreme Court.

The Republican plaintiffs argued that the universal, "no-excuse" mail-in ballot program passed by the Republican-controlled Pennsylvania legislature in 2019, enabling voters to cast ballots by mail for any reason, violated the state's constitution.

Biden won Pennsylvania by 80,000 votes and received a much higher proportion of the mail-in votes than Trump. Many more people voted by mail in 2020 because of health concerns prompted by the coronavirus pandemic as they sought to avoid crowds at polling places.

Reuters