An apparatus and method for restricting operation of a power delivery system are disclosed. In at least some embodiments, the apparatus includes a first input terminal at which is received a first command signal, and a second input terminal at which is received an additional signal. The apparatus further includes an output terminal at which is provided a control signal, and a circuit that generates the control signal based at least indirectly upon the first command and additional signals. The control signal generated by the circuit is configured to cause the power delivery system to not deliver at least one type of power when the first command signal indicates a command to do so, if the additional signal indicates an acceptability status. In some embodiments, the power delivery system is an isolation system (e.g., safety isolation system) as are employed in industrial environments, and the apparatus is a permissive module.