The UK Environment Agency has banned staff travelling by air for journeys in England and Wales.
It has also stopped air travel to destinations served by Eurostar.
The Yorkshire-based Agency said air travel would only be permitted in exceptional cases. These include travel to islands, like the Isles of Scilly or offshore locations.
Any travel by air will have to have approval from the one of the organisation's senior directors.
It said the change in policy would save about 30 tonnes on carbon a year.
The Agency, whose remit is to protect the environment, said it had already cut 11m miles (24%) from staff travel over the last four years.
It also encourage staff only to travel when necessary and then to go by train.
Dr Paul Leinster, the Agency's CEO, said: "We aim to lead the way on environmental performance.
"Our restriction on domestic air travel builds on previous and continuing action on business mileage, energy use, waste to landfill and renewable energy generation.
"It's another important step in reducing our carbon emissions."
www.environment-agency.gov.uk