Control of access authorisation for a working vehicle

The system has keys comprising mechanical coding and designed for accessing a motor vehicle (2). The keys comprise identification characteristics read by a radio frequency identification-transponder. One of the keys is formed as a main key (8) that is attached to the motor vehicle, such that the read characteristics of the main key are assigned to the vehicle. The characteristics of another key are assigned to the motor vehicle by programming the latter key, where the motor vehicle has an anti-theft device (10) that is released by the characteristics of the keys. An independent claim is also included for a method for controlling access authorization for a motor vehicle.