Lawyers for President Donald Trump sent a cease-and-desist letter to his former senior strategist Stephen Bannon, arguing he had violated a non-disclosure agreement in speaking about his time on the campaign and in Trump’s most trusted inner circle.

In a letter sent Wednesday night, Trump’s lawyers told Bannon his comments to author Michael Wolff in a soon-to-be-released tell-all book violate Bannon’s employment agreement that he signed with the Trump Organization in numerous ways and also likely defame the president. They ordered that he stop communicating either confidential and or disparaging information, and preserve all records in preparation for “imminent” legal action.

“You have breached the Agreement by, among other things, communicating with author Michael Wolff about Mr. Trump, his family members, and the Company, disclosing Confidential Information to Mr. Wolff, and making disparaging statements and in some cases outright defamatory statements to Mr. Wolff about Mr. Trump, his family members, and the Company,” read the letter from lawyer Charles Harder.

In a statement late Wednesday, Harder said Bannon’s expansive comments about Trump and his family to Wolff expose him to “numerous legal claims including defamation by libel and slander, and breach of his written confidentiality and non-disparagement agreement with our clients. Legal action is imminent.”

A representative for Bannon had no immediate comment on the letter.