After days of research, I can find no legal authority for ICE or CBP to require passengers to show identification on an entirely domestic fight.There is much more, and I encourage you to head over and read the whole thing.
...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."
...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. ...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.