The present document defines the stage 1 specifications of the Barring of Incoming Calls (BIC) supplementary service for the Trans-European Trunked Radio (TETRA). Stage 1 is an overall service description from the users point of view but does not deal with the details of the human interface itself. The present document specifies the service description of the supplementary service and the procedures to be expected with successful and unsuccessful outcomes. In addition the present document specifies the interactions with other TETRA supplementary services and inter-working considerations. Charging principles are outside the scope of the present document. The