Private property = their rules, including the on site parking facility. It is that simple.
Bucking the company rules or a decision leaves one open to sanctions all the way to dismissal for cause.
In the area of firearms this is true. Kind of shame that anti-discrimination laws continue to leave such a huge hole that allows gun owners to be so treated.
I can accept a libertarian argument against anti-discrimination laws.
Or, I can accept that no discrimination for lawful, peaceful, non-disruptive personal attributes or behavior should be permitted.
What really rubs me the wrong way is that anti-discrimination favors certain groups and certain traits/behaviors while leaving other groups and trait/behaviors out in the cold.
Apologies for the off-topic rant on this thread.
To come back onto topic a bit, "parking lot preemption" to protect employees against negative employment action for lawful items stored in their private cars parked in the company parking lot seems to me to be a workable compromise. Employers still control their property materially, but do not get to reach into a private employee's car. Employees are not disarmed for their commute or other pre or post work activities, nor for what they do over the lunch hour.
Obviously, this requires legislation which probably doesn't make it past your current governor.
Charles