(I am assuming) that your place of employment in private property. That being the case, they have the legal right to tell you "no weapons". Just as they have the legal right to fire you if you are caught violating their company policy.
Your CCW permit only allows you to carry "in public", and any private property that informs you that you cannot carry there is entirely within their rights. Stores, workplace, resturants, they have the right, and the legal authority to forbid weapons, open, or concealed.
This is NOT a violation of your constitutional rights. Your right to bear arms does not trump the right of property owners. Just as their rules do not trump your rights on your property.
No one is forced to work there. No one is forced to go there. You can leave, or simply not go there at all. Now, it may be extremely inconvienient for you, but that has nothing to do with your, or their rights.
My opinion is that since they deny you the ability to carry a weapon, they are morally responsible for your safety. However, they are not legally responsible, beyond what OSHA requires for a safe workplace. And, given their policy, it appears that it is their belief that forbidding weapons to employees is the best solution for worker safety.
You may be a calm, stable, rational individual, and so may 99% of the workforce be, BUT, if even one employees is not, and harms another with a weapon that the company "allowed" on the premises, they will be held liable in court. Or at least someone will try to hold them liable in court. Either way, the company is at risk of losing a significant amount of money in fees and judgements. SO, the absolute ban, in order to protect their bottom line.
If you carry concealed in a (private) place that does not allow it, they cannot have you arrested for that. But they can order you to leave, and have you arrested for tresspass, if you do not comply. Your employer, CAN fire you for violation of company rules, provided you are informed of the rules (which you obviously are) just as they can fire you for stealing company property.
Its a bit sad, but the fact is you don't have a legal leg to stand on, when it comes to CCW at work. Their place, their rules. Period.
State law allows your permitted carry anywhere public, excepting bars and banks. Seattle recently tried prohibiting lawful CCW in their parks, and got overruled by the courts. They are currently trying to justify their position and get the ban re-instated, but at the moment that has not happened.
The best advice I can give you is to obey their rules, and run the risk until you can find another employer with a more tolerant attitude (which means you should be looking). I know jobs are scarce these days, and the advice of "move" or "find another job" isn't something easily done, or practical, very often. But you ought to consider it. No job is worth your life.
All else being equal (and it almost never is) bigger bullets tend to work better.