A better model may be a guild like actors have (SAG).
Certain 'base-level' protections are agreed to with regards to health and safety, working hours, perhaps minimum salary guidelines, healthcare, retirement plans/pensions (?), etc. However things like salary can be independently determined. Paying dues would also give access to employment lawyers and dispute resolution mechanisms.
Just as (e.g.) SAG makes sure everyone on set is safe (both Tom Cruise and Jane Smith who plays Waitress #2), but people can be paid according to their (perceived?) importance to the project.