(CNN) Aviation police officers in Chicago are sitting targets for potential terrorists because they don't carry guns and are told to run and hide in the event of an attack, the union representing the officers said Thursday.

Matt Brandon, the secretary-treasurer of SEIU Local 73, warned city officials that the terrorist attack in Turkey is a "clear signal from international terrorists that they intend to kill and maim people in airports across the world."

In a scathing letter to Aviation Department Commissioner Ginger Evans, Brandon wrote, "Imagine if you will, the video recorded by cameras in Chicago's airports showing aviation police officers running alongside panicked and helpless travelers with a suicide vested terrorist pursuing them intent on killing as many of them as possible."

CNN investigation in December revealed that the nearly 300 aviation police officers at O'Hare and Midway airports are not only unarmed, but they are instructed to "run and hide" in the event of an active shooter. Officers repeatedly told CNN that the policy puts them in danger.

JUST WATCHED Airports ramp up security in wake of Istanbul attack Replay More Videos ... MUST WATCH Airports ramp up security in wake of Istanbul attack 01:19

The aviation police officers work for the Chicago Department of Aviation and are all certified law enforcement officers in the state of Illinois. Many also work in suburban police departments or are military veterans.

Read More