Methods and apparatus for controlling the transmission of user data over an NAS of a telecommunications network. An AMF includes a receiver configured to receive NAS policy control data determined by a PCF. The NAS policy control data identifies a user, is based on the user's subscription to the telecommunications network and includes one or more authorization parameters identifying whether the user is permitted to transmit user data over the NAS. The receiver also receives from a UE, or an AS, an NAS transmission request identifying the user and requesting transmission of user data over the NAS. An NAS transmission authorizer controls whether the transmission of the user data over the NAS should be authorized based on the authorization parameters and the NAS transmission request.