Let's not forget that there are unions for highly skilled labor as well. When I was a classical musician I belonged to a very robust and very helpful musician's union. Everyone I know _always_ had a preference for union gigs as they usually paid better and ensured that you didn't have to deal with all sorts of nonsense from your employer (like rehearsals running overtime, not getting paid in a timely manner, blind auditions, etc).

Professional classical musicians require a great deal more training (and talent) than programmers to get to the level where they can make a living doing it.