Your definition of union is completely different from this conversation's definition of union. I wasn't even aware of your definition of union until I intervie

Your definition of union is completely different from this conversation's definition of union. I wasn't even aware of your definition of union until I interviewed at this company that made software for unions as you describe them. Those unions are indeed exactly as you describe, and that company's customers used the company's software for tracking work of their union members, which were at what level of competency, even dispatching jobs, and so on. They were indeed tradesmen and craftsmen. The unions discussed in this conversation are collective bargaining units that negotiate employment agreements with a single employer, and such negotiations are often huge, nasty, and difficult. I went through such a dispute with a telecom, and everyone not unionized had to work as a scab (doing the job of those who were unionized and not working). The union people would picket outside our building and insult us when we went for lunch, and we pulled 80 hour days to do their work (with fortunately amazing OT pay, and I was part of a team in charge of trying to automate everything in sight). But it was a nasty dispute. The current NHL lockout that's happening is another similar union dispute, though you obviously don't see NHL players picketing NHL headquarters. :)