Describes requirements for apparatus incorporating facilities for barring certain outgoing calls or classes of outgoing calls to a public switched telephone network. Applies to apparatus where the decision to bar a call is undertaken either by means within the apparatus or by other means external to the apparatus. Does not apply to mechanical attachments that restrict operation of the dial or keypad. Does not apply to apparatus for connection to shared service lines or 1+1 carrier systems or as extensions to any form of private branch exchange or between the Test Jack Frame and the lines of the PBX. Covers definitions, connection arrangements, functional requirements, electrical requirements, marking and information to be provided by the supplier.