Tom Steyer’s lawyers sent a breach of contract letter on Friday to Fox News Channel demanding that the network start running his ads urging viewers to sign an online petition telling Congress to impeach President Trump.

Brad Deutsch of the Washington, DC, offices of the Garvey, Schubert & Barer Law Firm sent a letter dated November 3 claiming that Fox News had unconditionally accepted payment on October 27 to run Tom Steyer’s “advertisement” for a second week.

According to Deutsch, Fox News “abruptly” pulled the ad without explanation on October 31, “after unconditionally accepting payment” to run more national ads. He warned Fox News that its action was not only a “baseless and unethical” breach of an agreement, but also “a profound failure of journalistic integrity, a suppression of constitutionally protected speech and likely a consequence of inexcusable political pressure.”

Deutsch noted that other Fox-owned television stations continued to run the NeedToImpeach.com advertisement.

Steyer’s attorney did praise what he referred to as the “principled exercise of editorial discretion” by ABC, NBC CBS and CNN for refusing to carry President Trump’s ad “touting the first 100 days of his presidency and impugning the mainstream media as ‘fake news.’” But he claimed that Fox News’ decided to pull Steyer’s ad President Trump “threatened retaliation against broadcasters who provide him with negative coverage.”

Steyer’s $10 million ad campaign covered every major U.S. metropolitan market by signing up all the major TV networks, Facebook and YouTube. Steyer stars in his own ad, in which he argues that the President Trump has obstructed justice and his actions risk thrusting the U.S. into a nuclear war.

But Fox News co-president Jack Abernethy confirmed to the San Jose Mercury News in a statement that the network had pulled the ad because of viewer backlash: “Due to the strong negative reaction to their ad by our viewers, we could not in good conscience take their money,” he said in a statement.

Steyer went on MSNBC’s top Friday night show, All In with Chris Hayes, to complain that Fox News had “refused to fulfill their contract with us.” He speculated on-screen that Fox News was either scared either by a Trump tweet storm or a direct “request from the White House.”

Thomas Steyer & Kathryn Ann Fahr LLC/Tom Steyer of San Francisco, CA was the “top individual” contributor in the 2016 election cycle. One hundred percent of their $91,149,980 donations went to Democrats and liberal campaigns, with nothing to Republicans and conservatives. Steyer and his wife were also the top contributors in 2014, with $75,455,634 going exclusively to Democrats and liberal campaigns.

Steyer told the Business Insider shortly after the election that he was “surprised and disappointed” by Hillary Clinton’s loss. But he promised to double down on his millennial outreach to formulate an effective plan for Democrats and liberals to succeed in 2018 and 2020. He is also rumored to be considering a challenge to Sen. Diane Feinstein (D-CA) in 2018.