ICE Arrested a Man in Oregon Without a Warrant. Senators Want to Know Why.

Both of Oregon’s senators have demanded an explanation after Immigration and Customs Enforcement agents in plain clothes entered a home in Portland without a warrant and arrested a man who was later released.

The arrest of the man, who was working on a renovation at the house on Thursday, was captured on a cellphone video by a co-worker who published it on Facebook, where it was viewed more than a million times.

News of the encounter spread, and United States Senators Ron Wyden and Jeff Merkley, both Democrats who had previously voiced concerns about how ICE is operating in their state, said the arrest “appears to be an illegal entry of a private home,” according to a joint letter sent on Friday to a regional director at the agency.

The video, which is more than seven minutes long, begins after three ICE agents are already inside the house. One of them asks the man, identified by the senators as Carlos Bolanos, for his identification. The man asks why.

“I have reason to believe you are not in the country legally,” the agent replies.

The co-worker recording the cellphone video, George Cardenas, then asks the agents why his colleague is being arrested and what the charges are, but none are specified. He asks them repeatedly to identify themselves and tells the agents they are trespassing, but the one agent who speaks throughout the encounter says the house is a place of business, apparently because the two men are working inside.

Mr. Cardenas says that the homeowners live in the furnished basement, and points out their car.

“If you guys don’t have a warrant, you’re kind of breaking the law,” Mr. Cardenas said. “Well, you are breaking the law, basically, at this point.”

The video records a back and forth over access, and Mr. Cardenas agrees that he opened the door when he saw the agents outside but says he did not give them permission to enter. At one point, the agent says, “We don’t need to introduce ourselves by our names.”

After several minutes, the agents arrest Mr. Bolanos, removing a paintbrush from one hand and a cellphone from the other and then placing his hands behind his back and handcuffing him. He is walked to a car outside.

An ICE public affairs officer, Yasmeen Pitts O’Keefe, said later that Mr. Bolanos was released from custody pending further investigation. She said in a statement that the matter had been referred to the ICE Office of Professional Responsibility and the Department of Homeland Security’s Office of Inspector General.

“The agency is reviewing this incident,” Ms. Pitts O’Keefe said. She did not reply to a request for further comment on Monday.

In their letter to Elizabeth Godfrey, a deputy field office director for ICE, Mr. Wyden and Mr. Merkley wrote that people “do not lose their constitutional protection from warrantless search and seizure simply because ICE believes they may be immigrants.”

The senators asked Ms. Godfrey for an explanation of the policies that led to Mr. Bolanos’s arrest and questioned whether the behavior of the agents conformed to guidelines. Mr. Cardenas said on Monday that Mr. Bolanos planned to speak with a lawyer before talking publicly about the episode.

It was the latest encounter to bring ICE under criticism for its agents’ practices during arrests in Oregon and across the country. The letter from the senators said that the encounter with Mr. Bolanos came about two weeks after ICE responded to their questions about the targeting of an American citizen in Hillsboro, Ore.

In that episode last month, according to an account by the American Civil Liberties Union, a man, Isidro Andrade-Tafolla, and his wife were stopped by ICE agents as the couple left the Washington County Courthouse.

Mr. Andrade-Tafolla was asked to show his identification by agents who did not identify themselves, but who showed him a photograph. Mr. Andrade-Tafolla said that it was not him in the photograph, and that the only resemblance was skin color.

“That confusion about who is who with unidentified ICE agents could literally become deadly,” Sheriff Pat Garrett of Washington County said at a news conference last month after Mr. Andrade-Tafolla was stopped. He said sheriffs in Oregon had expressed concern to ICE about other circumstances in which agents did not identify themselves or drove in unmarked cars.

“We have heard story after story,” Representative Suzanne Bonamici said at the news conference in September.

“Without a response, we will assume that an investigation into the Washington County incident is not underway,” the lawmakers said. “Now after this most recent incident, it is even more disturbing to witness ICE agents act inappropriately again, only a month later.”

Mat Dos Santos, the legal director for the A.C.L.U. of Oregon, said in an interview over the weekend that the arrest of Mr. Bolanos, as seen in the video, was “flagrantly unconstitutional.”

“I hope that they review this incident and realize just how bad it is and how plainly illegal this arrest was and reprimand and retrain officers on how to conduct an arrest legally,” he added.

“I don’t have a lot of hope for that,” he said. “It’s an agency that operates largely in secret and with little public oversight.”