The "buffer zones" around red squirrel sites in northern England have been widened after the plight of the species was raised in parliament.
Red squirrels are threatened by a virus carried by greys
Environment minister Lord Rooker said Natural England had taken the measures on a "precautionary basis" to limit the encroachment of grey squirrels.
It comes after the Forestry Commission called for greater protection for reds.
Northumberland, Cumbria and Merseyside are the north's last strongholds for red squirrels.
The UK's native species has dwindled since greys were introduced in the 19th Century and rapidly dominated food supplies and habitats.
The larger North American squirrels also carry a pox which is fatal to reds.
Natural England is responsible for licensing the release of greys, though only about six have been released since 2006.
Last month, Liberal Democrat peer Lord Redesdale - chairman of the Red Squirrel Conservation Partnership - claimed the group had wiped out two thirds of Northumberland's grey squirrels.