The city of Atlanta is suing 18 discount online travel companies — including, Expedia Inc., Orbitz and — claiming that they could owe the city millions of dollars in unpaid taxes.

The complaint, filed Wednesday in Fulton County Superior Court, claims that the online companies routinely charge local hotel-motel taxes to customers who reserve rooms online. But, according to the suit, the online firms pocket that money instead of remitting those tax dollars to the city or county government where the hotel or motel is located.