Why wouldn't they be fired? Their employer is setting a working standard within their organization. If the employer states "drug free workplace" and you come in stoned out of your mind, you'd expect not to get fired? This is no different.
If your employee states that you can't wear a hat to work and by doing so you may risk termination....go ahead and wear the hat, you're gonna get canned.
Deal with it and move on, boomer.