Recently the National Rifle Association has been lobbying for states to pass laws forcing private companys to allow firearms on their property. They feel that a gunowner should at least be allowed by his employer to keep a gun in a locked compartment in his own vehicle.
Constitutional rights apply to the relationship between the individual and the government, not between labor and management. When a guy exercises his First Amendment right to call his boss a jackass to his face, he usually gets fired for it. Likewise, the right of private business to restrict workers, venders, and customers from bringing guns onto the property should be upheld.