Washington (CNN) A top aide to former Defense Secretary James Mattis sued the Pentagon this week, claiming the Defense Department deliberately delayed the publication of a book detailing his time in the Trump administration so that Mattis' own memoir can be released first.

Guy Snodgrass, a former Navy pilot who served as Mattis' communications director and chief speechwriter, claims the Defense Department is "obstructing and infringing" of his First Amendment rights by "intentionally" withholding final classification approval for his manuscript titled: "Holding the Line: Inside Trump's Pentagon with Secretary Mattis."

In a lawsuit filed Thursday, Snodgrass says the Defense Department office that screens books set for publication has slow-walked his manuscript, demanded the author redact entire chapters, and threatened him with retaliation for violating an unspoken loyalty oath to Mattis.

"This obstructive delay by the Defense Department has gone on long enough and needs to come to an end," Bradley Moss, a lawyer for Snodgrass, told CNN.

"The First Amendment rights of Mr. Snodgrass are no less significant than those of Mr. Mattis, and with this lawsuit we intend to ensure Mr. Snodgrass can lawfully tell his story about what he observed during his service just like Mr. Mattis is about to do," he said.

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