A top aide to former Defense Secretary James Mattis filed a lawsuit Thursday claiming the Pentagon is "obstructing and infringing on his right" to publish a memoir about his 17 months in the Trump administration.

Guy Snodgrass, a longtime Navy pilot who worked as Mattis' communications director and chief speechwriter, claims the Defense Department has "unreasonably delayed" reviewing the manuscript for his memoir, "Holding the Line: Inside Trump's Pentagon with Secretary Mattis."

In the suit, filed early Thursday, Snodgrass claims the Pentagon has "intentionally withheld" final approval of his manuscript so that Mattis' memoir, "Call Sign Chaos: Learning to Lead," could be published first. Mattis' book is scheduled to be released on Sept. 3.

Snodgrass, citing unnamed sources inside the Pentagon, also says the delay has been done "with the acquiescence, if not complicity of" Mattis.

CDR Guy Snodgrass, USN. U.S. Naval Institute

Sue Gough, a spokesperson for the Defense Department, said the department did not comment on ongoing litigation.

"Holding the Line," originally scheduled for publication on Oct. 29, will need to be pushed back, Snodgrass claims in the 10-page suit, arguing that the Defense Department has violated his First Amendment right to free speech.

Snodgrass, who departed the Pentagon last August, claims that the Pentagon has "unlawfully demanded the redaction of wholesale chapters that it has acknowledged are unclassified" and "implicitly threatened" him with potential "retaliation were he to violate alleged loyalty oaths sought" by Mattis.

Mattis, through his publisher, did not immediately respond to a request for comment.

The government is only permitted "to safeguard classified information," said Mark Zaid, Snodgrass’s attorney. "The reality appears to be that [Pentagon] officials were deliberately slow-rolling the process in order to ensure Mattis' book is published first."

In one specific claim, Snodgrass says that he told Mattis about his memoir via email in late March, and that Mattis allegedly responded: "I regret that you appear to be violating the trust that permitted you as a member of my staff to be in private meetings in my office," where involved parties believed they could "speak openly."

Snodgrass, citing news reports, counters that Mattis' book "hypocritically contains his recollection of private and official conversations with the political and military leadership of the United States, to include the President, ostensibly in violation of the very loyalty and trust he sought to impose."

A press release from March said Snodgrass had penned a "sometimes shocking" book detailing the "complicated relationship" between Mattis and President Donald Trump, describing how the former secretary worked to block some of the president's proposals.

The press release said Snodgrass provides a "fly-on-the-wall view of Mattis" during critical national security events and crises, including "learning about major policy decision via Twitter, rather than from the White House" and how Mattis "slow-rolled some of Trump's most controversial measures, with no intention of following through."

"Holding the Line" is the first book by one of Mattis' closest advisers, and is the first look behind the scenes of Mattis' nearly two-year tenure as defense secretary.

Mattis, a former Marine Corps general, rarely engaged with the media and kept a lower profile than previous defense secretaries. He resigned in December after Trump announced an immediate U.S. withdrawal from Syria.

In an interview with The Atlantic's Jeffrey Goldberg published online this week, Mattis said of his decision to resign: "I had no choice but to leave."