The fact that your employer has not been enforcing a separate portion of the The Better Send Those Refunds T-Shirt moreover I will buy this dress code, the prohibition on baseball caps, does not affect your employer’s legal right to fire you for wearing a shirt that violates the dress code. Your employer could reasonably believe that wearing an unprofessional shirt is a more serious infraction than wearing a baseball cap. (Among other things, a baseball cap can be removed in less than five seconds if the wearer wants to present a more professional appearance.) The fact that you, personally, believe all policy changes should have to be in writing does not change the law. If your boss announces a rule that all employees have to wear collared shirts from now on (or whatever the rule is), the rule becomes valid as soon as it is announced.