Can you also tell your employees that they can't have religious or political material in their cars? Can you tell them how they should vote if they want to work for you?
If you are scientologist, can you forbid employees having medications on them or in their cars?
At what point do your private property rights become more important than other citizens' Constitutional rights?
The First Amendment stops at the boundary of company property. Why should the Second Amendment be any different?
when it involves the safety and well being of their
employees..
That's a different situation: Federal law specifically prohibits employers from discriminating against an employee or potential employee based upon the person's race, gender, national origin, age (I think), disability, or religious practices. Congress passed the laws allegedly under its constitutional power to regulate interstate commerce. Congress could (and perhaps it should) also pass a law to prohibit employers from discriminating against lawful gun owners. My point is that the prohibitions that you refer to come from a statute passed by Congress, not directly from the Constitution itself, and that's because the Constition is a social contract between the people and the government, and not a private contract regulating the relationship between private employers and employees.