Cliff Sims, a former communications aide in President Donald Trump's White House and the author of the recently released tell-all book "Team of Vipers", is now suing his former boss for allegedly trying to punish him for publishing his story.
But Sims did sign an NDA for his work on the Trump campaign.
Sims is suing Trump in his official capacity.
Sims' lawsuit comes after the Trump campaign filed an arbitration claim against the White House aide turned author.
Michael Glassner, who leads the Trump campaign, did not immediately respond to a phone call seeking comment.
The lawsuit requests a court ruling that Trump "may not enforce, whether directly or through non-U.S. Government cutouts, any nondisclosure agreements that seek to unconstitutionally infringe upon his First Amendment rights".
Attorney Mark Zaid tweeted that his firm was representing Sims pro bono, adding that the suit was an effort "to ensure no Presidential Administration, whether GOP or DEM, can silence former federal employees from discussing unclassified aspects of their public service". He signed a nondisclosure agreement.
Trump has had members of the administration and his campaign sign non-disclosure agreements, as revealed by Omarosa Manigault-Newman, who wrote a scathing book about her time working for Trump after she was sacked.
Sims's lawsuit notes it does not seek to stop those proceedings, which it states will be handled separately.
Trump has previously come under scrutiny for his use of NDAs to prevent current and former employees from speaking out against him.
According to The Times, the lawsuit claims that Trump is "seeking to impose civil liability against Mr. Sims through the application of NDAs that apply to information Mr. Sims learned exclusively during his federal service".