CCW's are "contracts only" with the issueing authority to carry a weapon concealed in public areas. Private property, no matter what requires permission from the owner to carry that weapon concealed or otherwise, after all the property owner did not issue your CCW, there for does not have to honor it.
Then, relating to your question, there is major liability of a business or employer who denies the right to self protection these days when work place terrorism is a real danger. Especially if they do not have an armed guard or guards who can without delay protect anyone within split seconds, meaning, if there are few guards at a guard shack, and there is a big plant without guards patroling and being able to response to any threat, anywhere in the plant within seconds, you have em by the balls. Give the BAR time and they will screw this one down the toilet.
Here in Florida a CCW is not required to have a loaded handgun in your private conveyance (auto)as long as it is concealed from view. No permit required to carry concealed or open on privately owned property even if it business property, as long as the owner gives their permission. An occasional police type not knowing what the law is, will often be held liable, for arresting one in possession a handgun without a CCW on business or private property, that actually had permission from the owner of the property to possess the handgun on their property. Many simply do not understand that controls (codes & laws) implaced on their private property or business that deny the right of self protection are null and void, and many cases prove this as fact (a good reference is http:www.fsdf.org/deadly-force.htm
Long guns, shot guns, machine guns while not part of this subject, can be carried loaded anywhere in your auto, as long as it is not concealed, and on private property including a business, with the owners permission.