A control system and a related method includes determining an access state of a vehicle and communicating a locking command message from an off-board control system to remotely change the access state of the vehicle between a locked state and an unlocked state. In the locked state, an operator is unable to one or more of access a location of the vehicle, access an area internal to the vehicle, change a power setting of a component of the vehicle, or engage a propulsion system of the vehicle. The operator onboard the vehicle may be prohibited from changing the access state from the locked state to the unlocked state without assistance from the off-board control system, but the operator may be allowed to change the access state from the unlocked state to the locked state without assistance from the off-board control system.