Representatives of students, military service personnel, civil service personnel, prisoners, patients and people on placements cannot be elected as employee representatives or as members of the working environment committee unless provided for in supplementary regulations. Nor do they have voting rights in connection with elections of safety representatives and members of working environment committees, and they shall not be reckoned with when deciding whether the number of employees in the undertaking indicates that a working environment committee must be established, unless otherwise provided for in supplementary regulations.