Giuliani has been at the forefront of pushing the unsupported allegation that Biden, while vice president, urged the firing of Ukraine’s top prosecutor in March 2016 to benefit his son Hunter Biden, who was on the board of a major energy company in the country.

The Obama administration, along with other Western nations, the International Monetary Fund and Ukrainian reformers, supported the firing of then-prosecutor Viktor Shokin, who was seen as not aggressively pursuing corruption cases.

Giuliani appeared on Sunday on ABC’s “This Week” and CBS’s “Face the Nation,” with the shows’ hosts, George Stephanopoulos and Margaret Brennan, respectively, among the recipients of the letter from the Biden campaign.

The letter was sent to more than a dozen TV news executives and journalists, including the presidents of CNN (Jeff Zucker), Fox News (Suzanne Scott), MSNBC (Phil Griffin), ABC News (James Goldston), NBC News (Noah Oppenheim) and CBS News (Susan Zirinsky), and hosts such as CNN’s Jake Tapper, NBC’s Chuck Todd and Fox News’ Chris Wallace.

A CNN spokesperson declined to comment about the Biden campaign’s letter. Representatives from Fox News, MSNBC, ABC, NBC and CBS did not immediately respond to requests for comment.

The Biden campaign has aggressively pushed back on reporting of the Ukraine allegations in hopes of not making the same mistakes as Hillary Clinton’s team in responding to coverage of email controversies that dogged her candidacy.

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Over the course of an hour on Sunday evening, Giuliani fired back with half a dozen posts on Twitter.

“Joe and Hunter Biden are clearly rattled by the affidavit showing there is a named accuser and not an anonymous source,” he tweeted , without giving any details. “The Bidens have played the influence game for years and now the American people are demanding answers!”

Regarding the letter from the campaign, he said : “Think of the Biden arrogance and entitlement to protection. They believe they own the media and they are demanding that they silence me. They know I have incriminating facts, not hearsay, because they know what they did in selling Joe’s office to a Ukrainian crook.”

Though political campaigns are known to dispute coverage they consider unfair, it’s rare to demand that a specific guest not appear on air.

In the letter, the Biden team argued that “Giuliani is not a public official, and holds no public office that would entitle him to opine on the nation’s airwaves.” And so, they continued, “the decision to legitimize his increasingly outlandish and unhinged charges and behavior — calling it ‘news’ — rests solely with you."

The campaign applauded hosts for pushing back on Giuliani’s claims in real time, but suggested that it wasn’t enough.

“Giving Rudy Giuliani valuable time on your air to push these lies in the first place is a disservice to your audience and a disservice to journalism,” they wrote. “We ask that you no longer book him on your air.”