U.S. citizens, many of them Latino men, have been stopped and in some cases taken into custody by law enforcement officers who are carrying out President Trump’s immigration crackdown and who suspect the men are living in the country illegally.

While many of those detained have immediately declared their U.S. citizenship to officers, they have routinely been ignored, according to interviews with the men, their lawyers and court documents. In some cases they have been handcuffed, kept in holding cells and immigration facilities overnight, and in at least two cases held without access to a lawyer or even a phone call.

How many U.S. citizens have been swept up in the Trump administration’s immigration sweeps is difficult to say. No comprehensive log of such encounters is available from the federal government, and immigration agents are not required to document stops of citizens.

A review by The New York Times of publicly reported cases and court records found that since January, at least 15 U.S. citizens have been arrested or detained and questioned about their citizenship by immigration agents or local law enforcement officers enlisted to work with the federal authorities.

In late January, Julio Noriega, 54, of Chicago, had been handing out copies of his résumé to local businesses in Berwyn, Ill., when ICE officers approached him as he walked out of a Jiffy Lube auto service shop.

They handcuffed him and loaded him into a van, without allowing him to explain he was a citizen, according to a motion filed in the Federal District Court for Northern Illinois. He was released about 10 hours later, the court filing states.

Kenny Laynez-Ambrosio, 18, was born and raised in West Palm Beach, Fla., where he lives with his mother and two brothers.

He was on his way to work with his mother and two friends in May when troopers from the Florida Highway Patrol stopped them in their employer’s pickup truck for what the agency said was a “commercial motor vehicle inspection.” Initially, Mr. Laynez-Ambrosio was calm, he recalled in an interview. But the situation escalated as troopers learned that others in the car were undocumented and ordered everyone out.

When no one got out of the vehicle, the troopers began to pull the three men out. At one point a trooper fired a Taser at one of them.

Mr. Laynez-Ambrosio, recording on his phone, repeatedly told the officers, “I’m from here!”

“You’ve got no rights here. You’re illegal, brother,” a trooper is heard saying. In Florida, a new state law requires all local and state law enforcement agencies, including the Highway Patrol, to participate in immigration enforcement.

All three men were taken to a nearby Border Patrol facility, and though Mr. Laynez-Ambrosio continued to say he was a citizen, he was held there for about six hours.

Asked about the U.S. citizens identified by The Times, the Department of Homeland Security defended its actions as “highly targeted.”

“If and when we do encounter individuals subject to arrest, our law enforcement are trained to ask a series of well-determined questions to determine status and removability,” Tricia McLaughlin, a department spokeswoman, said in a statement.

Federal officers’ tactics remain a source of contention in the courts. This summer, the American Civil Liberties Union filed a lawsuit against the federal government, arguing that the roving patrols are targeting Latinos and violating the Fourth Amendment, which protects against “unreasonable searches and seizures.” A federal judge in Los Angeles ordered a halt to stops based on a person’s apparent race or ethnicity, or other factors that suggest they are Latino, such as speaking Spanish or accented English.

But this month, the Supreme Court put the order on hold. The lawsuit will still make its way though the lower courts and may end up back at the Supreme Court. In the meantime, federal agents in and around Los Angeles will not be constrained by the lower court’s finding that such stops were unconstitutional.

Immigration enforcement agents have for decades focused on workplace raids or targeted unauthorized immigrants in order to arrest them for deportation. But during some immigration sweeps in heavily Latino communities, particularly in Southern California, federal agents have roamed the streets, courthouses and workplaces demanding proof of citizenship from residents. The roving patrols and impromptu interrogations have been a striking departure from the understanding that the Constitution allows citizens to remain silent and places limits on who officers can question, hold and detain.

As videos of these encounters have spread online, many Latino men and women who are citizens have begun to carry their passports as they go about their daily lives, fearful that they too will be stopped and questioned by immigration agents.

A report by the Cato Institute found that a substantial number of ICE actions have targeted workplaces and neighborhoods that are heavily Latino. One in five of the agency’s arrests has been of a Latino resident with no criminal past or removal order, according to Cato, a prominent libertarian think tank, which analyzed ICE arrest records obtained through the Deportation Data Project.

In upholding a lower-court ruling against the government, the U.S. Court of Appeals for the Ninth Circuit cited the experience of Jason Brian Gavidia, 29, who was born in California, the son of Salvadoran and Colombian immigrants. Mr. Gavidia, who refurbishes old cars, was raised in East Los Angeles, where Latinos make up the overwhelming majority of the population.

According to videos of the encounter, interviews and court records, officers did not identify themselves as they entered his auto business in Montebello, Calif., in June, masked and with guns drawn. They wrestled another owner, Javier Ramirez, 32, to the ground, holding him at gunpoint, and pushed Mr. Gavidia against a fence.

“The agents repeatedly asked Gavidia whether he is American — and they repeatedly ignored his answer: ‘I am an American,’” the ruling stated.

The officers, who were from Customs and Border Protection, an agency of the Department of Homeland Security, took Mr. Ramirez away in a van, driving him around for hours before taking him to a federal detention center downtown, according to a statement he submitted to the court. Mr. Ramirez did not speak to a lawyer or any family member for three days, he said in an interview.

Asked about the men’s cases, D.H.S. has said that Mr. Gavidia interfered with their enforcement operations and that Mr. Ramirez assaulted officers. But Mr. Gavidia was never charged, and a charge against Mr. Ramirez was dropped. Security videos of the incident reviewed by The Times do not show Mr. Ramirez assaulting officers.

In several of the cases, D.H.S. officials told The Times that the citizens assaulted officers; prosecutors have not pursued charges in any of those incidents.

As Mr. Trump campaigned for re-election, promising to carry out the largest deportation effort in the nation’s history, he often cited as a model a 1950s initiative named after a racial slur, “Operation Wetback.” In the decades since, federal courts have ruled that immigration agents cannot detain people without having a specific, factual basis for believing a person is in the country illegally.

The Supreme Court emergency ruling earlier this month effectively allows agents to stop anyone on suspicion of being an immigrant living in the United States illegally.

George Retes Jr., 25, a U.S. Army veteran who works as a security guard at Glass House Farms in Camarillo, Calif., said he had been trying to report to work in July as people protested an immigration sweep. He said that he tried to explain to officers that he was not involved with the demonstration and needed to get inside, but that he received conflicting instructions from the officers. He said he got back in his car and tried to reverse as some officers directed, but protesters were massing behind his vehicle.

Federal officers then deployed tear gas on the crowd, broke his windshield, cast pepper spray on his face and took him into custody, he said. “As they’re walking me away, I’m telling them: ‘I’m a U.S. citizen. I’m American. I’m a veteran. I didn’t do anything wrong,’” he said.

He was held for three days without a phone call.

In an essay published this month in the San Francisco Chronicle, Mr. Retes reiterated that he was wrongfully detained and warned that what happened to him could happen to “any one of us.” In a response to the essay, the Department of Homeland Security wrote on X that the arrest of Mr. Retes during the raid was “for assault.” A spokesman for the U.S. attorney’s office in Los Angeles said they filed a complaint but later asked the court to dismiss the case, which it did.

In August, a 15-year-old U.S. citizen with developmental disabilities was sitting in a car with his mother outside a high school in Los Angeles as his cousin registered for classes when agents surrounded him at gunpoint. The 15-year-old was handcuffed for several minutes before agents let him go, according to an interview with his lawyer and a claim filed with federal immigration authorities.

Asked about the case, immigration officials said they had been in pursuit of a man from El Salvador with gang ties. In their claim, lawyers for the boy, identified only as B.G., contend they racially profiled a Mexican American citizen and put his family in danger.

The tactics and the results have raised questions even among some who support the administration’s overall approach on immigration.

“If you’re going to be aggressive on deportations in the interior, you cannot make a mistake,” said Daniel Garza, a former police officer who backed Mr. Trump and heads the Libre Initiative, a conservative group focused on Latino voter outreach. “If people are being stopped solely because of the way they look, that is a problem.”

Leonardo Garcia Venegas, who was born in Florida, said that in May he tried to keep going about his work at a construction site in Foley, Ala., when he saw immigration agents shove his brother, who is undocumented, to the floor.

He pulled out his phone to film and was quickly tackled to the ground by other officers, Mr. Venegas said. They kept him in handcuffs for hours, claiming his identity documentation was fake, he said. A spokeswoman for D.H.S. said that Mr. Venegas tried to physically obstruct immigration officers; no charges were filed and he said he stood filming from several feet away.

More than a month later, at another construction site in Fairhope, he was confronted again, Mr. Venegas said. This time, agents didn’t handcuff him, he said, but they again questioned his citizenship, escorted him out and held him for at least half an hour.

“I cannot work in peace anymore,” Mr. Venegas said in an interview. “I am always nervous.”

Indeed, for Americans caught up in the immigration dragnet, those encounters can remain visceral memories, even as they move on with their lives.

Miguel Angel Ponce Jr., 33, said he still feels paranoid after what happened to him in July. Mr. Ponce was driving to work in Houston when, he said, he was pulled over by ICE agents just minutes from his house. He was not told why he was being arrested, only that he looked like someone they were looking for. He was cuffed, placed in the back of their car and driven to a parking lot nearby, where he remained for over two hours.

A D.H.S. spokeswoman said Mr. Ponce was “temporarily taken into custody by mistake,” adding that once the agents confirmed he was not the person they were after, “they took him back to his residence and apologized for the confusion.”

Kitty Bennett contributed research.