HAYWARD (CBS / AP) — Authorities said a masked man wielding a semi-automatic pistol forced the employees of an East Bay Jack in the Box into a refrigerator before robbing the restaurant.

It was the third Jack in the Box robbery in Hayward since May 1, and the second at that particular franchise.

Police Sgt. Mark Ormsby said officers responded late Monday to a 911 call from an employee reporting an armed robbery at the restaurant on Mission Blvd.

The suspect took $500 from the cash registers and ran out of the store. Nobody was injured.

During a May 1 holdup at that same Jack in the Box, two suspects wearing ski masks ordered all the employees into the kitchen.

Police are investigating whether any of the robberies are related.

(Copyright 2013 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)