Protecting rights is a valid function of govm't. Just as protecting employee health is a valid concern, so is protecting their right to travel to and from work with any legal item in their vehicle, or on their person. The employer demand an item not be brought into the workplace, but he has no right to demand it not be in their vehicle.
Well, here you are disallowing the *right* of the business owner to control what happens in his own parking lot.