United States President Donald Trump’s lawyers sent a cease-and-desist letter to his former strategist Steve Bannon on Wednesday, threatening legal action for violating a non-disclosure agreement, The Guardian reported.

The legal notice was sent after Bannon allegedly defamed the president by speaking to author Michael Wolff. His book Fire and Fury: Inside the Trump White House has stirred a major controversy with allegations that the president was unprepared for his job, and that Bannon thought a meeting between Donald Trump Jr and a group of Russians during the 2016 presidential election campaign was “treasonous”.

“You have breached the agreement by, among other things, communicating with author Michael Wolff about Trump, his family members, and the company, disclosing confidential information to Wolff, and making disparaging statements and in some cases outright defamatory statements to Wolff about Trump, his family members, and the company,” read the letter from lawyer Charles Harder, according to the Washington Post.

Bannon has also reportedly referred to Ivanka Trump as “dumb as a brick”, and said that the president found the White House “vexing and even a little scary”.

Trump responded by saying that Bannon “lost his mind” when he lost his job in August. Instead of ranting on Twitter as usual, the president released a statement that said Bannon has nothing to with him or his presidency. “Now that he is on his own, Steve is learning that winning isn’t as easy as I make it look,” Trump said.

“Steve pretends to be at war with the media, which he calls the opposition party, yet he spent his time at the White House leaking false information to the media to make himself seem far more important than he was,” Trump’s statement added. “Steve was rarely in a one-on-one meeting with me and only pretends to have had influence to fool a few people with no access and no clue, whom he helped write phony books.”