You have absolutely every right to refuse to serve alcohol especially with states having dram shop acts and of course the increased risk to the person himself or herself and to others when drunk. You cannot be fired for such an act and if you are terminated for such an act, you have a viable claim for wrongful termination despite any at-will employment laws. You need to consider speaking with local labor law counsel if indeed you were terminated and make sure you are not waiting on any unemployment claims during this time, either.