The actor Justin Baldoni filed a defamation lawsuit against the Hollywood stars Blake Lively and Ryan Reynolds on Thursday, claiming that they tried to destroy him by accusing him of sexual harassment against the actress and then retaliation against her through a smear campaign.

The lawsuit is the latest legal action in a feud tied to the 2024 film “It Ends With Us,” which starred Ms. Lively and Mr. Baldoni, who also directed it.

The 179-page complaint, filed in the U.S. District Court for the Southern District of New York, named Ms. Lively and Mr. Reynolds, her husband, as defendants, as well as their publicist Leslie Sloane and her company, Vision PR. The lawsuit was filed on behalf of Mr. Baldoni; the film’s lead producer, Jamey Heath; their production company, Wayfarer Studios; and the publicists Melissa Nathan and Jennifer Abel. They are seeking $400 million in damages.

In response to the lawsuit on Thursday, Ms. Lively’s legal team said in a statement, “The strategy of attacking the woman is desperate, it does not refute the evidence in Ms. Lively’s complaint, and it will fail.”

The New York Times published an article on Dec. 21 about Ms. Lively’s allegations against Mr. Baldoni. She claimed in a complaint, filed a day earlier with the California Civil Rights Department, that Mr. Baldoni had initiated the campaign after she accused him of sexual harassment during the shooting of “It Ends With Us.”

The Times report referred to private text messages and emails that Ms. Lively had obtained through a subpoena and that had been included in her complaint.

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