If you are in an area of the employer which is not open to the public, you have no “right” to do or possess (or say, or that matter) anything which the employer prohibits. If you are in a “public” area owned by the employer (i.e., not on anyone’s private, controlled property), then you do have rights which can be adjudicated.
Many of the problems in this area of “rights” stem from employee use of parking lots which are also used by the public. There are some employers who have tried to prohibit employees having guns in their cars while not exercising the same restriction against non-employees, which is certainly unfair and perhaps even unlawful in some jurisdictions.
“If you are in an area of the employer which is not open to the public, you have no “right” to do or possess (or say, or that matter) anything which the employer prohibits.”
Among other things:
As written, that means I have no right to say “no” to a sexual proposition if the employer prohibits saying “no”.
As written, that means I have no right to do anything to defend myself against being raped if the employer prohibits my doing anything to prevent it.
Are you sure your statement as written is something you want to, or even can, defend?