Giant African land snails (GALS) in Norwegian is Afrikanske kjempesnegler.
The importation of ALL foreign land snail species to Norway requires a permit.
Link to the law in English (government.no/regjeringen.no)
Link to the law in Norwegian (lovdata).
Link to more information in Norwegian (Miljødirektoratet/Norwegian Environment Agency).
This law is quite new (implemented 01.01.16), which has lead to some packages without a permit number getting through. That said, it is still irresponsible and illegal to import land snails into Norway without a permit. If it is caught by customs, the snails will either be destroyed or returned to sender.
It is the receiver of the snails (the one who is in Norway) who has to apply for the permit.
You apply here.
The permit number must be clearly visible on the package. A good place to write it is directly under the name and address.