That's the best part! They don't have to fire you with a reason, at-will employment means they can just fire you and you're going to have to prove in court it could
only have been because you were talking about your salary. Good luck!
You just show up to the office, your fob doesn't work, and security walks out to inform you that you don't work here anymore and to expect an email from HR.
(Will a good company do this? No. Could they if they wanted to, and totally get away with it? You bet!)