Authorities say four people were removed from a Chicago-bound plane at Baltimore-Washington International Thurgood Marshall Airport at the captain’s request.

Maryland Transportation Authority Police spokesman 1st Sgt. Jonathan Green said Tuesday that Spirit Airlines flight 969 was taxiing to the runway when the flight crew determined that the plane needed to return to the gate. He says the captain asked police to remove four people, three men and a woman, from the plane and police are investigating.

Airport spokesman Jonathan Dean says a passenger “reported that another passenger may have made a comment or exhibited other unusual behavior.”

The flight was scheduled to leave at 6 a.m. It has not departed.

(AP)