Sen. Mark Kelly, D-Ariz., filed a lawsuit Monday against Defense Secretary Pete Hegseth and the Pentagon, charging their effort to censure and demote him is “unlawful and unconstitutional.”

Hegseth said last week that the Pentagon was taking steps to downgrade Kelly’s military retirement rank and pay because of his “seditious statements” — a reference to a video he and other retired service members released that urged members of the military not to comply with illegal orders.

The suit charges Hegseth’s actions violate Kelly’s First Amendment rights, as well as the Speech and Debate clause of the Constitution, which grants immunity to lawmakers for official acts.

“It appears that never in our nation’s history has the Executive Branch imposed military sanctions on a Member of Congress for engaging in disfavored political speech,” says the suit, which seeks a court order declaring Hegseth’s actions to be unlawful.

“Pete Hegseth is coming after what I earned through my twenty-five years of military service, in violation of my rights as an American, as a retired veteran, and as a United States Senator whose job is to hold him—and this or any administration—accountable,” Kelly said in a statement. “His unconstitutional crusade against me sends a chilling message to every retired member of the military: if you speak out and say something that the President or Secretary of Defense doesn’t like, you will be censured, threatened with demotion, or even prosecuted.”

The Pentagon did not immediately respond to a request for comment.