Why are Hollywood unions so powerful?

Alex Tabarrok asks and answers.

One thing I think he doesn't emphasize enough: the entertainment unions have been clever enough to give their members no incentive to defect. Unlike in many unions, top members are not slaves to seniority or scale. The unions set a floor on talent pay that is low enough that it does not come out of the pay of the stars. The ultimate cost of the high union scale is probably paid by consumers of extremely low budget indie films that now have to be made without union talent; this makes the cost of unionization the next best thing to invisible, and college students with excessive tattooing are at any rate not a very powerful constituency against a union.