The hell they can't. One of my co-workers got pulled over coming into work back in '06, they asked if they could search his car, he said no, they pulled him out of the vehicle, zip-tied him and put him face first on the curb while they tore his vehicle apart. He had zero criminal record and obviously wasn't carrying anything, early-20s Indian computer geek. They broke several things on his vehicle and they zip tied him so tight that he had marks on his wrists for several days.
I don't know if they had a false tip, bad indigestion from eating indian food, or what, but they were total pricks, made him almost 2 hours late to his shift, but at least we were able to see why he was late.