Wisconsin's Supreme Court on Monday rejected a legal challenge from President Trump's campaign seeking to overturn President-elect Joe Biden's victory in the key battleground state.

A majority decision from the state's high court said that the Trump campaign had failed to show that more than 220,000 votes were illegally cast and should be invalidated.

"The Campaign is not entitled to relief, and therefore does not succeed in its effort to strike votes and alter the certified winner of the 2020 presidential election," Justice Brian Hagedorn wrote for the majority.

The court ruled 4-3 that the campaign's challenges to certain categories of ballots in Milwaukee and Dane counties were either without merit or should have been brought long before Trump lost the election.

"The Campaign's delay in raising these issues was unreasonable in the extreme, and the resulting prejudice to the election officials, other candidates, voters of the affected counties, and to voters statewide, is obvious and immense," Hagedorn wrote.

"Our laws allow the challenge flag to be thrown regarding various aspects of election administration," the judge added. "The challenges raised by the Campaign in this case, however, come long after the last play or even the last game; the Campaign is challenging the rulebook adopted before the season began."

A spokesman for the Trump campaign did not immediately respond when asked for comment.

The lawsuit was seeking to disqualify absentee ballots that were cast in person, from people who claimed to have been "indefinitely confined," that were collected by poll worker at a public park in Madison and those where elections officials filled in missing information on ballot certifications — a policy that has been in place since 2016.

The ruling came just an hour before Wisconsin's slate of electors are set to meet and officially cast the state's 10 Electoral College votes. Biden won Wisconsin, which went to Trump in 2016, by about 20,000 votes.

His victory was certified last month after a partial state recount verified and even extended his lead over Trump.