A professional is in sort of a weird position union-wise though. He often is part of some organization of professionals. That organization doesn't negotiate one employment contract for all (or even large portions of) its members, but it does have a lot of sway over whether he can be hired in that profession and give him a convenient higher power to support his refusal to commit some sort of professional misconduct. "Union" definitely has the wrong connotation though.

Not really. There are unions for jobs like writing and teaching I'd consider pretty squarely "professional."