Elephants brought in from the countryside are rented to people who walk under their stomachs - considered to bring good luck - or who use them to carry signs advertising ivory-carving businesses.
But city life is hard on elephants because of the heat and pollution, said the Society for the Prevention of Cruelty to Animals.
The elephants sometimes must eat garbage and drink dirty water, and they have nowhere to take their customary cooling-off showers.
The government sent an order to all Bangkok districts telling officials they must eject any big animals in their areas, including elephants.
Violators could be fined up to $20.