Adding a name to the no-fly list requires “credible information demonstrating that the individual presents a threat of committing an act of terrorism,” according to the Terrorist Screening Center, part of the FBI. The list, a subset of a much larger database, is used by the Transportation Security Administration to screen air passengers.
In 2016, California Sen. Dianne Feinstein disclosed that the no-fly list then numbered about 81,000 people, with fewer than 1,000 U.S. citizens. The larger database included about 1 million people, 99.5% of whom were foreign nationals, she said.
The exact criteria for the no-fly list has been criticized by the American Civil Liberties Union as “impermissibly vague.”