Not only does a company NOT have that Right, they would be commiting a federal crime (deprivation of civil Rights) by doing so.
They have no more legal ability to ban their employees from having guns than they have to not pay social security taxes.
Let me rephrase that: "if a company were to decline to hire anyone who did not sign an affidavid stating that they did not own any firearms..." Any prospective employee would have the right to find such a policy objectioanle and walk out the door. And any current employee who at any time found such a policy objectionable would likewise be free to hand in walking papers and leave as well.
If I don't own a gun, and I decide to spend all my money on things other than firearms, my right to own a gun doesn't mean I can reasonably demand to be given one, nor does my lack of money mean I don't have a right to own a gun. The right to own a gun doesn't guarantee that one can do so without giving up other non-rights (like a year's worth of cable TV). If I decide the cable TV is more important than a firearm, it's my right to make that decision. I'll still have the right to get a gun as soon as I decide it's important enough for me to give up some other things so I can afford it.