Former Secretary of Defense Mark Esper, who served under former President Donald Trump until his firing in the wake of the 2020 election, has sued the Department of Defense over redactions they made to his upcoming book.

Esper’s memoir, set to be released in May of 2022, is expected to chronicle his time in the Trump administration, in which he served first as Secretary of the Army and then as Secretary of Defense until Trump tweeted about his firing on Nov. 9, 2020, following weeks of contention.

The lawsuit, filed in the U.S. District Court in Washington on Sunday, said that Esper engaged in “extensive coordination” with the Department’s Office of Pre-publication and Security Review.

Esper alleges the review “dragged on” for six months and when he finally heard back on Oct. 7 after reaching out in May, there was no explanation given for some redactions.

“No written explanation was offered to justify the deletions,” Esper wrote in an e-mail to current Defense Secretary Lloyd Austin. “My follow-on conversations with the DOPSR official handling my case confirmed my assessment. He similarly has been unable to assert that the redacted items contain classified information or compromise national security.”

Esper said he was asked not to quote his conversations with Trump or other foreign officials, although much of the material “was already in the public domain,” according to Esper.

His attorneys argue in the lawsuit that the Defense Department “has unlawfully imposed a prior restraint upon Mr. Esper by delaying, obstructing and infringing on his constitutional right to publish his unclassified manuscript entitled ‘A Sacred Oath.'”

The former defense secretary also said he had already met with Austin’s chief of staff and the Defense Department’s Director of Administration and Management, Mike Donley.

“I should not be required to change my views, opinions, or descriptions of events simply because they may be too candid at times for normal diplomatic protocol. After all, the DOPSR process is about protecting classified information and not harming national security — two important standards to which I am fully committed. Moreover, my Constitutional rights should not be abridged because my story or choice of words may prompt uncomfortable discussions in foreign policy circles,” he said in the suit.

Pentagon press secretary John Kirby responded in a statement on Monday.

“We are aware of Mr. Esper’s concerns regarding the pre-publication of his memoir. As with all such reviews, the Department takes seriously its obligation to balance national security with an author’s narrative desire. Given that this matter is now under litigation, we will refrain from commenting further,” Kirby said.

In a memo reported first by ABC News Chief Washington Correspondent Jonathan Karl in his new book “Betrayal,” the Presidential Personnel Office under the direction of John McEntee, a favorite aide of Trump, made a case for firing Esper three weeks before Esper was terminated.

Reasons outlined for his firing in the memo included that Esper “barred the Confederate flag” on military bases, “opposed the President’s direction to utilize American forces to put down riots,” “focused the Department on Russia,” and was “actively pushing for ‘diversity and inclusion.'”

ABC News’ Matt Seyler contributed to this report.