Okay, I’m glad you said this first. I’ve taken Employment Law and Commercial Law (which covers UCC articles 2, 3 and 9) and I had no idea what OP was talking about. I suppose it could be in one of the articles of the UCC in theory, it just didn’t make sense that it would be. So I agree, there shouldn’t be anything about employment law in the UCC.
Some states put up some legislative barriers (talk to a lawyer before you fire anyone in California), but I think at-will is possible, if not the default, in every state.
(oh, and not to be that guy, but right-to-work usually means no closed-shop unions).