Brittany Ferries is reported to have abandoned plans to fit new engines to several of its ships because of the cost involved.
The company had planned to spend £320 million on fitting the engines to six of its ships because of new EU regulations on sulphur emissions.
The ferries would have run on liquefied natural gas, which is less polluting than the heavy fuel oil used today.
Instead, the company plans to switch the ships to diesel fuel and fit filters to funnels to clean emissions.
It also cancelled the order of a new ferry, which would have run on liquefied natural gas, the BBC reported.
Brittany Ferries announced the planned changes to the ships, which link Portsmouth, in Hampshire, Poole, in Dorset, and Plymouth, in Devon, with Spain and France, in August.
But the company now says the cost cannot be justified. New EU regulations on sulphur emissions come into force in January.