U.S. Rep. Doug Lamborn announced Monday that he plans to join more than 100 other House Republicans in contesting the vote count from six states when Congress convenes later this week to certify the election of President-elect Joe Biden.

“Congress must closely and thoroughly examine the allegations of voter fraud and take appropriate steps to restore trust in the election process,” Lamborn said in a statement declaring he will object to certifying electoral votes cast by Arizona, Georgia, Pennsylvania, Wisconsin, Nevada and Michigan – all states won by Biden.

Citing what he described as “last-minute changes” made to election procedures amid the COVID-19 pandemic, the Colorado Springs Republican, who was elected Nov. 3 to his eighth term, said that his constituents “deserve to know that the 2020 election was free of fraud.”

President Donald Trump, who lost the Nov. 3 election to Biden by more than 7 million votes and 306-232 in the Electoral College, has been claiming for months that widespread voter fraud and irregularities cost him a second term despite no credible evidence emerging that happened.

The election results have been certified in all 50 states and the District of Columbia, and the former vice president is set to be sworn in as president on Jan. 20. Biden carried Colorado by 13.5 points, marking the fourth time in a row that a Democrat has won the state’s nine electoral votes.

Said Lamborn: “A free and fair election system is one of the fundamental building blocks of our republic. As a Member of Congress, I took an oath to uphold the Constitution and the rule of law. The serious irregularities and improprieties marring the 2020 general election threaten America’s confidence in our electoral system.”

State and federal officials have said the 2020 election was conducted safely and securely. The president and his allies have filed nearly 60 lawsuits challenging the results, including before the U.S. Supreme Court, but almost all have been dismissed or dropped.

Through a spokeswoman, Lamborn declined an interview request. The congressman also wouldn’t say whether he considers Biden the president-elect, didn’t cite any evidence of fraud or specific irregularities that led him to question the election results and refused to answer questions about his record supporting election security measures.

Congressional leaders of the effort to overturn the election said this weekend that they expect as many as 140 House Republicans to raise objections on Wednesday when the House and Senate meet in a joint session to tally the electoral votes. At least a dozen Republican senators have also said they’ll object, forcing a vote in the two chambers, though neither is expected to reverse Biden’s win.

The Associated Press reported Monday that prominent Republicans are pushing back against what some describe as a “scheme” to keep Trump in office.

“The 2020 election is over,” said a bipartisan group of 10 senators, including Republicans Bill Cassidy of Louisiana, Susan Collins of Maine, Lisa Murkowski of Alaska and Mitt Romney of Utah. Their statement argued that attempts to cast doubt on the election are “contrary to the clearly expressed will of the American people and only serve to undermine Americans’ confidence in the already determined election results.”

Efforts to cast doubt on the election results “strike at the foundation of our republic,” said former House Speaker Paul Ryan, a Wisconsin Republican, in a statement calling Biden’s win “entirely legitimate.”

Rep. Liz Cheney of Wyoming, the third-ranking House Republican, wrote Sunday in a memo to colleagues that the objections “set an exceptionally dangerous precedent, threatening to steal states’ explicit constitutional responsibility for choosing the President,” arguing that the effort is “directly at odds with the Constitution’s clear text.”

Lamborn, an honorary co-chair of Trump’s Colorado campaign, is the last GOP member of the state’s congressional delegation to reveal his position on challenging the election. He joins fellow Republican U.S. Rep. Lauren Boebert, who was sworn into office Sunday and announced in December that she will object to Biden’s win.

U.S. Rep. Ken Buck, the chairmen of the Colorado GOP, said in a statement issued Sunday by seven GOP lawmakers that they will not be challenging the results, citing constitutional provisions the conservatives argue prevent Congress from doing anything other than counting electoral votes submitted by the states.

Lamborn and Buck in December signed on to a brief supporting a Texas attempt to overturn the election results, but the U.S. Supreme Court quickly dismissed th lawsuit.

The Associated Press contributed to this report.

This developing story has been updated.