Of course you can.
Employers in the USA however, -- are limited by our fed/state/local laws, -- on the rules they can set. --
-- Our supreme Law of the Land says the right of the people to carry and own arms shall not be infringed. -- And this principle applies to all of us, employees or employers.
Banks routinely prohibit firearms in their buildings. How do distinguish banks from employers— in a legal sense? Under your way of thinking, banks are violating constitutional rights when they don’t let you bring guns to the teller window. Employers can do the same thing. I tend to agree, perhaps, that employers SHOULD not have these rules, but they are allowed to. If you disagree, laws can be passed to require employers to allow guns to be owned and/or carried by employees.