A new law has come into effect in Mexico City giving the authorities the power to fine shops which give away free plastic bags to their customers.
In future, shops in the Mexican capital will have to charge for the bags, which must also be biodegradable.
As well as fines of up to $90,000 (£57,700), shop owners not complying can be given a 36-hour jail term.
A local official said the law was part of the city's "Green Plan" and aimed to raise awareness of the environment.
"This won't happen overnight," Leticia Bonifaz Alfonso told the Efe news agency.
Officials estimate that people in Mexico City at present use more than 20 million plastic bags per day. They are blamed for many health and environmental hazards.
Efforts in cities across the world are being made to reduce the use of plastic bags.
The bags are made mostly from polyethylene, a derivative of petroleum. When discarded, they can take hundreds of years to decompose.