Passengers on a domestic flight from San Francisco to New York received an unusual greeting when they landed at JFK Airport Wednesday night: two Customs and Border Protection agents waiting on the jet bridge to check IDs as people exited the aircraft.

VICE News staffer Anne Garrett was on the flight and documented the incident. It triggered outrage and concern on Twitter, with Edward Snowden and other prominent civil liberties advocates speculating that it could be linked to President Trump’s new hard-line policies on immigration.

Customs and Border Protection (CBP) later confirmed the details of the incident. In a statement to VICE News, a spokesperson for the agency said the agents were present because Immigration and Customs and Enforcement (ICE) had asked for help locating an individual “ordered removed by an immigration judge.”

“To assist our law enforcement partners, two CBP officers requested identification from those on the flight in order to help identify the individual,” the CBP statement said. “The individual was determined not to be on the flight.”

Garrett, a video editor at VICE News who was traveling for personal reasons, said the incident occurred as passengers disembarked Delta Airlines flight 1583 from San Francisco. According to Garrett, shortly after the plane landed, at about 7:45 p.m., a member of the flight crew announced over the plane’s intercom that all passengers would have to show their “documents” to CBP officers in order to exit the aircraft.

“People were like, ‘What does that mean? Do I need to show my ticket?’” Garrett recalled. A few moments later, Garrett said, a flight crew member clarified that passengers would need to show their passport or another form of government-issued identification.

Garrett said two CBP agents in blue uniforms were waiting as she stepped off the plane and onto the jet bridge. She offered her driver’s license and asked for more information but did not receive a response.

“I said, ‘Why do you need to see this?’ He just took it out of my hand,” Garrett said. “It’s a tough situation to be in because everybody wants to get off the flight. You don’t want to be the one holding up the line.”

A Delta spokesperson said the airline had contacted CBP “to get a sense of why their presence was needed,” but offered no additional comment on the incident.

A division of the Department of Homeland Security, CBP has about 60,000 agents stationed at airports and border crossings around the country, and the agency routinely questions travelers arriving in the U.S. from overseas. It’s unusual, however, for passengers aboard a domestic flight to be scrutinized after landing.

The Transportation Security Administration (TSA) asks domestic travelers to show ID in order to clear airport security checkpoints, but U.S. citizens are not legally obligated to comply. TSA agents will typically pull such travelers aside for additional screening and ask a series of questions to verify the person’s identity.

“CBP should explain why one of its officers was apparently demanding that passengers on a purely domestic flight show ID,” said Hugh Handeyside, a staff attorney at the ACLU’s National Security Project. “CBP is not an always-and-everywhere police force, and any attempt to expand its operations beyond its authority would raise serious concerns.”

Handeyside noted that the ACLU is currently putting together a “Know your rights” guide to educate travelers about how to respond if similar incidents occur in the future.

CBP has been on the front line of President Trump’s immigration crackdown. Its agents were tasked with enforcing Trump’s executive order that banned travel to the U.S. by people from seven Muslim-majority countries. That measure was later suspended by a federal judge, but the Trump administration has vowed to issue another similar order soon.

Trump has also issued executive orders that expand Homeland Security’s “enforcement priorities,” allowing ICE and other agencies to indefinitely detain virtually anyone suspected of being in the country without authorization. The orders have led to stepped-up enforcement by ICE in recent weeks, but the incident Wednesday is the first known incident where federal authorities questioned domestic air travelers over an immigration issue.