Chicago city officials are scrambling to contain a controversy over the city's red light camera system, which may have issued thousands of tickets under questionable circumstances.

An investigation by the Chicago Tribune revealed dramatic increases in the number of tickets issued at a dozen intersections in recent years. City officials have not been able to explain the surges, and a number of aldermen are calling for an investigation by the city's inspector general.

Mayor Rahm Emanuel has promised to refund the fines for any of the 13,000 tickets involved that are shown to be unjustified. But some aldermen are calling for removal of the 11-year-old camera system, which they say is designed more for raising revenue than protecting public safety.