I asked two experts whether I had missed some general exception to the Fourth Amendment for passengers on a domestic flight. After all, passengers on flights entering the U.S. from other countries can expect to be asked for ID, and even searched. Barry Friedman, the Jacob D. Fuchsberg professor of law and affiliated professor of politics at New York University, is the author of Unwarranted: Policing Without Permission, a new book-length study of intrusive police investigation and search practices. “Is this remotely constitutional?” he asked. “I think it isn’t. We all know generally the government can’t come up and demand to see identification.” Officers need to have statutory authority to search and reasonable suspicion that the person to be searched has violated the law, he said. Andre Segura, senior staff attorney at the American Civil Liberties Union’s Immigrants’ Rights Project, told me that “I’m not aware of any aviation exception” for domestic passengers.

An ID check is a “search” under the law. Passengers on the JFK flight were not “seeking admission”—the flight originated in the U.S. CBP officials told the public after the fact that they were looking for a specific individual believed to be on board. A search for a specific individual cannot include every person on a plane, regardless of sex, race, and age. That is a general paper check of the kind familiar to anyone who has traveled in an authoritarian country. As Segura told me, “We do not live in a ‘show me your papers’ society.”

I asked a CBP spokesperson what legal authority the agency could show for the search. In response, the spokesperson said:

In this situation, CBP was assisting ICE in locating an individual possibly aboard the flight that was ordered removed from the United States pursuant to the Immigration and Nationality Act. To assist ICE, CBP requested consensual assistance from passengers aboard the flight to determine whether the removable individual in question was in fact aboard the flight. In the course of seeking this assistance, CBP did not compel any of these domestic passengers to show identification. With much-appreciated cooperation from these passengers, CBP was able to resolve the issue with minimal delay to the traveling public.

It's quite legal for law enforcement to ask for “voluntary” cooperation. Anyone who follows criminal-procedure cases, however, knows that “voluntary” in legalese does not mean what ordinary people think it means. Supreme Court caselaw makes clear that officers may block an exit and ask for ID or permission to search. They aren’t required to tell the individual stopped that he or she may refuse, and they have every incentive to act as if refusal may result in arrest. The Supreme Court held in 1984 that “while most citizens will respond to a police request, the fact that people do so, and do so without being told they are free not to respond, hardly eliminates the consensual nature of the response.” Passengers deplaning after a long flight might reasonably fear they will be “detained” if they anger the law enforcement figure blocking their exit. That officer is under no obligation to tell them they can refuse.