A Wildlife Rescue Centre says it will have to euthanise grey squirrels that come into its care, after change in the law.
As of October it will be illegal for wildlife hospitals to release grey squirrels and other indigenous species including Muntjac deer and Canada geese back into the wild.
The rules mean sanctuaries will either have to look after the animals for the rest of their natural lives or euthanise them.
Grey squirrels have rapidly spread since they were introduced into this country 150 years ago, displacing the native red squirrel. They are now regarded as a pests, as they damage trees and pass on a virus which has further reduced red squirrel numbers.
Now the Department for Environment, Food and Rural Affairs, will implement an EU regulation which forbids wildlife centres from releasing them back into the wild.
But animal hospitals like Vale Wildlife Centre say they will not have enough room to keep dozens of grey squirrels for the rest of their natural lives, so euthanasia may actually be the only option.
The Gloucestershire Wildlife Trust is developing a strategy to discourage grey squirrels. One idea is the introduction of pine martens which will prey on them. The predator have been introduced in other parts of the country and red squirrels are returning.