“We are writing today with grave concern that you continue to book Rudy Giuliani on your air to spread false, debunked conspiracy theories on behalf of Donald Trump,” two top Biden campaign advisers—Anita Dunn and Kate Bedingfield—wrote in the letter.

Giuliani is a “surrogate” for the president, who has demonstrated that he will “knowingly and willingly lie” in order to advance his own narrative and often contradicts himself “multiple times over the course of an answer,” the letter argues, before then listing some examples.

“This morning on CBS, he attacked the credibility of the former Ukrainian prosecutor on whom he has previously staked most of his harebrained case against Biden when the prosecutor said definitively he believed there was nothing here to investigate,” the letter explained. “He’s certainly not introducing new facts, since his relationship with the truth is casual at best.”

Newsweek reached out to Biden’s 2020 campaign for further comment but did not receive a response in time for publication.

News about the letter was first reported on by The Daily Beast. Giuliani responded to the document in a statement sent via text message to the publication, where he called the move “usual left wing censorship.” “Everything I say is supported by such as today, affidavits and statements,” the attorney added. “They are the ones who have covered up pay for play for at least 5 years.”

Brad Parscale, the manager of Trump’s 2020 reelection campaign, responded to the letter by mocking both the Democrats and cable news in a tweet. “Can we request the removal of Democrats on TV that push hoaxes? Wait, but then who would do the interviews?” he wrote, alongside a link to the Beast’s report.

Although such a move by a presidential campaign is rare, Giuliani has made numerous appearances on cable network shows in recent days to peddle debunked theories about Hunter Biden, the former vice president’s son, and his alleged ties to Ukraine.

This weekend, the president’s attorney said that unless Democrat Adam Schiff is removed as chairman of the House Intelligence Committee, he would not cooperate with the panel’s probe into allegations of Ukrainian quid pro quo involving Trump. Giuliani also continued to condemn Biden and his son for what he called a “very serious sell-out of public offices” during a Sunday segment on ABC News’ This Week.

Giuliani has crafted numerous narratives live on-air about Trump’s innocence after House Speaker Nancy Pelosi announced a formal impeachment inquiry into the president on Tuesday. On Saturday night, he indicated to Fox News host Jeanine Pirro that it might have been unlawful if he or Trump had not contacted Ukraine about their Biden allegations.