I have to side with Pizza Hut on this one.
It was their policy and it was known by the employee (presumably) that NOT having a firearm on store premises was a condition of employment. The employee had the obligation of either complying with company policy OR taking a job with a company which allowed carrying a weapon at work. Unfortunately, instances of workplace violence by employees has risen along with robberies, and most companies have weighed the liabilities and risks associated with employees carrying weapons and have decided to ban guns on premises. Other companies have decided that the risks to their employees from armed thugs mitigates allowing their employees to have a weapon. I would presume that those stores which DO allow employees to be armed do a background check, require a gun safety course to be passed, and also require a 'carry license' to have been issued beforehand.