If it had been any other symbol there would have been no problem. Your GM admitted that. I would ask him if wearing it is going to jeopardize your job. (as you prefer to wear it just as you have for the last ten years.) If he says yes you have grounds for a lawsuit.
The thing is that you are being persecuted for your beliefs. There are two roads you can go down. One, the way of the Lord, turn the other cheek and remove the cross. Or two, fight the ruling. If you choose to fight the ruling you will cause yourself and your bosses strife, but may in the end overturn the ruling. However, this would not be the wisdom that comes from heaven which is first of all peacefull. And would for sure be fighting a battle in your own strength. which is never wise.
I say, follow what your heart (not your emotions or intellect) is telling you to do?
If it were me, I would remove it.
God grant you wisdom,