You've met a few unions? It's not really feeling like you have any specific domain knowledge here, given how sparse and off-kilter all of your replies have been. If you have actual counter-examples of other unions that operate differently in that space, then just name them.
Stars. Their economically useful for the industry, but entirely irrelevant to union requirements outside of SAG. Bringing them up when discussing labor practices in the industry at large is essentially a non sequitur.
To your question, I was a member of IATSE Local 600 (Cinematographer’s Guild) as a loader, 2nd AC, digital utility and sometimes focus puller. I noted my union affiliation upthread. Members are explicitly allowed to work on non-union jobs, but there is an expectation that you call it in if the budget is over ~1 million. Below that, the union is not particularly interested in attempting to flip the show so no one cares.
(This is where I would call you out for your tone of ignorant self superiority, but I’ll just defer to the HN guidelines and let it drop)
