In an unprecedented move, a top official of President Trump’s campaign is threatening that the campaign will sue a former staffer who wrote a tell-all memoir about chaos in the White House and on the campaign trail.

“The Trump campaign is preparing to file suit against Cliff Sims for violating our NDA,” Trump campaign chief operating officer Michael Glassner tweeted Tuesday, quoting a tweet from Trump himself calling Sims a “mess” and saying that he “signed a non-disclosure agreement.”

A lawsuit by a presidential campaign to stifle a former staffer for a tell-all would be highly unusual, especially where the candidate won and is still occupying the White House.

The book – titled Team of Vipers – covers Sims’ time on the 2016 Trump campaign but also his tenure in the White House. Glassner was the deputy campaign manager of Trump’s 2016 campaign.

Sims is far from the first former Trump staffer to write a tell-all of his time behind the orange curtain. Omarosa Manigault wrote her own reveal on the Trump campaign and presidency (including the potentially dubious revelation that Trump wanted to be sworn in on a copy of the The Art Of The Deal), earning her much spite from the West Wing.

But Sims has the distinction of being the first staffer whose tell-all has elicited legal threats, whether they pan out or not.

Glassner did not immediately reply to an email requesting comment.

Sims replied to Trump’s “mess” tweet on CNN.

“Nice. There it is,” he said.