LOS ANGELES — In an attempt to determine who was behind the caravans that were bringing large numbers of migrants from Central America to the southwest border, the Trump administration created a list of activists and journalists whom they subjected to additional scrutiny when they entered the United States last year.

Federal immigration authorities faced criticism Thursday after an internal government document, obtained by NBC 7 San Diego, suggested that immigration activists and journalists were specifically singled out for extra screening at border entry points by the U.S. and Mexican governments.

Those on the list had traveled with the migrant caravans as they arrived in Mexican border cities from Central America to seek asylum.

Customs and Border Protection officials said they had identified people because they may have had information in connection to assaults against Border Patrol agents that took place last November and in January, but said that gathering this type of information was standard.

“CBP does not target journalists for inspection based on their occupation or their reporting,” Andrew Meehan, the agency’s assistant commissioner of public affairs, said in a statement, adding that CBP “has policies in place that prohibit discrimination against arriving travelers and has specific provisions regarding encounters with journalists.”

Nonetheless, the inspector general for the Homeland Security Department opened an inquiry last month, with CBP, “to ensure that all appropriate policies and practices were followed.”

Esha Bhandari, a lawyer with the American Civil Liberties Union, said that targeting reporters or advocates for secondary screening and extended detention on the basis of their work was a violation of their rights. Bhandari said the ACLU was monitoring developments in the cases and exploring all legal options.

“The implications of this are really disturbing,” she said. “It is unconstitutional for the government to target people for punishment or retaliation solely based on their First amendment-protected activity.”

Go Nakamura, a freelance photographer whose work has appeared in The New York Times and who was on the list, said he had suspected for several months that his name had been flagged to immigration officials.

On Thursday, he recalled being stopped by Mexican authorities in late December while he was near the border fence in Tijuana to take photographs of migrants. The officers asked to see Nakamura’s passport, something he had not experienced during other lengthy assignments on the border, he said. He thought it was strange when the officers took photos of his passport on cellphones.

Nakamura, an American citizen, tried to re-enter the United States several days later, and initially faced routine questions. He was asked about his background, where he lived, where he went to school. He was also asked about when he began working as a photojournalist.

But the questioning began to alarm Nakamura when an officer pulled out a document with pictures of about 10 to 14 faces and asked him to identify them.

“They asked me if I recognized any of the faces,” Nakamura said. “I didn’t, so I said no. The officer who showed me the papers, she was asking me if I was connected with the organizers of the caravan. She was like, have you met the organizers or do I know the organizers?”

“I felt like they thought I was a spy or something,” Nakamura said.

Kitra Cahana, a freelance photographer on the list whose work has also appeared in The Times, said she was barred from entering Mexico on Jan. 17 while she was en route to photograph another caravan of migrants traveling through the country. As she was about to board a flight from Montreal to Detroit, she scanned her passport at a pre-clearance machine, which printed out a picture with an “X over my face.” She was taken into secondary questioning in Montreal, but was ultimately allowed to board her flight.

In Mexico City, she was again detained. That time she was held for about 13 hours, she said, before being officially denied entry to Mexico.

Mexican authorities confiscated her U.S. passport and cellphone during that period. She was escorted to a flight back to Detroit. Later that month, on Jan. 26, she said she tried to cross into Mexico from Guatemala, and was denied entry.

Bhandari said there were specific rules outlined by the Justice Department that the government must follow when questioning journalists, which, she said, Customs and Border Protection may have violated.

“The existence of these dossiers can have a real chilling effect,” Bhandari said. “It can suggest to other journalists that if they dare to report on activists that are embarrassing to the United States government, you too can be singled out for this harsh treatment.”

This article originally appeared in The New York Times.