Michael Avenatti, lawyer for porn star Stormy Daniels in her suit against President Donald Trump, has been arrested on suspicion of domestic violence, police in Los Angeles say.
Celebrity news website TMZ said this followed a physical confrontation between the lawyer and a woman.
He denied the claim and was later released on $50,000 (£38,500) bail.
The lawyer represents Ms Daniels, who alleges she and President Trump had a brief relationship - a claim he denies.
Ms Daniels has sought to free herself from a non-disclosure agreement she signed before the 2016 election.
Mr Avenatti has called the allegations "completely bogus" and said he was confident he would be fully exonerated.
Speaking to reporters after leaving a police station, he said: "I have never struck a woman. I never will strike a woman. I have been an advocate for women's rights my entire career and I'm going to continue to be an advocate.
"I am not going to be intimidated from stopping what I am doing."
On Twitter, he also thanked "everyone who has reached out with supportive messages".
Thank you to everyone who has reached out with supportive messages and offers of assistance. It means the world to me. I have always been an advocate of women's rights and equality & I always will be. I will not be intimidated into stopping my pursuit of justice and what is right— Michael Avenatti (@MichaelAvenatti) November 15, 2018
The woman who made the allegations had "visible injuries" including bruises, according to an unnamed law enforcement official quoted by the Los Angeles Times.
Mr Avenatti's estranged wife, Lisa Storie Avenatti, gave a statement to the broadcaster NBC saying he had never been violent to her.
His first wife, Christine Avenatti-Carlin, also issued a statement on Wednesday, saying she had known Mr Avenatti for 26 years and describing him as "a loving, kind father to our two daughters".
"He has never been abusive to me or anyone else. He is a very good man," she said.
A frequent guest on TV talk shows and news programmes, Mr Avenatti has emerged as a fierce critic of President Trump, the BBC's David Willis in Los Angeles says.
At one point Mr Avenatti was publicly contemplating running for president himself in 2020, our correspondent adds.