CHICAGO, Dec. 18 (UPI) -- Airline passengers are being screened by psychological experts for dubious behavior at U.S. airports, including Chicago's O'Hare International Airport.

The federal SPOT program -- Screening Passengers by Observation Technique -- looks for hostile intentions and possible terrorists by observing people for signs of stress, fear and deception, the Chicago Tribune said. About 600 SPOT officers work in U.S. airports, the Chicago Tribune said.

"Attacking aviation remains very much on al-Qaida's radar," Kip Hawley, administrator of the U.S. Transportation Security Administration, told the Tribune. "So we aren't going to let them come to O'Hare or any other airport to case out the place, only to return later with a live bomb, without us sending out the message that it's not safe to come here if you are a terrorist."

Critics said the new program doesn't work, violates constitutional rights and could be used for racial, gender or religious profiling, the Tribune said.