Michael Wolff recorded his conversations with former White House chief strategist Steve Bannon and other members of President Donald Trump’s administration, Axios reported on Thursday.

Axios reported that Wolff has “dozens of hours” recorded from his discussions with Bannon, Trump’s former deputy chief of staff Katie Walsh and other officials, some of whom thought they were speaking off the record.

The Guardian on Wednesday reported, citing Wolff’s as-yet unpublished book “Fire and Fury: Inside the Trump White House,” that Bannon said Donald Trump Jr.’s meeting with a Russian lawyer in June 2016 was “treasonous” and “unpatriotic.”

In response, Trump claimed that Bannon “had very little to do” with his election win, and claimed Bannon “lost his mind” after he was “fired” from his White House job.

The White House claimed Wolff’s book, which depicted Trump’s campaign and administration as a chaos-filled endeavor run by self-interested staffers, is “filled with false and misleading accounts” and “trashy tabloid fiction.”

On Thursday, Trump’s attorney Charles Harder sent letters to the author and publisher of Wolff’s book demanding that they stop efforts to print and release the book, which is set to come out next week.

Harder claimed Trump’s legal team is “investigating numerous false and/or baseless statements.” Any recordings of Wolff’s conversations with former White House staffers quoted in his book would throw a wrench into efforts to dispute the allegations it contains.

New York Magazine on Wednesday published an excerpt adapted from Wolff’s book with an explanation of Wolff’s access to top administration officials: Wolff claimed that after Trump was sworn in, he took up “something like a semi-permanent seat on a couch in the West Wing” at Trump’s own encouragement.

According to New York Magazine, nobody in Trump’s administration was in a position to either sanction or revoke Wolff’s access, which was not restricted and had no conditions attached, and Wolff subsequently conducted more than 200 interviews.