when you are a BIG studio, and want to hire the best guys, they will only work if the union allows. and for the union to allow your production has to use professionals from all other unions (guilds).
And that reciprocates so many jobs that everyone i know pays (or are making ends-meet to pay) the union (most are something like 5k for actors, 20k for photo, per year).
But, small indie movies, just shoot for a couple days and nobody has any pay. They usually gets people with little experience via email chain and facebook noise.
Isn't there a minimum scale for wages required for any film? Or is it only if the film somehow becomes a "union" job?