The solution fair both to employers and employees is to let employees lock personal self defense weapons in their car parked on the employee parking lot. That way the employer can regulate what comes into the work building and the employee isn’t defenseless driving to or from work.
If the employer wants everyone disarmed inside, it should have security and limit access as a disarmed area seems to attract mass murders and angry ex-spouses.
I'm a 2nd Amendment purist, but I also believe in property rights and freedom of assembly. If an employer doesn't want firearm owners to work for them, or to transport their weapons onto company property, they have that right. Like all rights however, they come coupled with responsibilities, and a property owner who inhibits the ability of those on their property to defend themselves must assume responsibility for the safety and security of those on the property.