"This is a serious and illegal erosion of our basic civil liberties," ACLU deputy legal director Cecilia Wang said in a written statement."
CBP said in a public statement the day after the incident that it was contacted by ICE to help locate an individual "possibly aboard" the Delta flight, who was ordered removed by an immigration judge, according to the lawsuit.
"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, according to the lawsuit. "The individual was determined not to be on the flight."
The ACLU alleges that the CBP agents acting at the behest of ICE "violated the passengers' rights against unreasonable search and seizure under the Fourth Amendment." The lawsuit says the CBP officers have border search authority, but a document on its search authority does not provide authorization to search passengers arriving on domestic flights.
The lawsuit seeks a permanent injunction barring such checks in the future, as well as attorneys' fees.
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U.S. Customs and Border Protection agents' actions dealing with passengers getting off a Delta flight earlier this year has prompted an ACLU lawsuit.