Well, unfortunately the major VFX houses today are not unionized. There used to be some, but Marvel opened the floodgates to contracting out major VFK work to non-union companies.

I imagine this will be added to the list of grievances animators historically have had with the lack of union protections in recent years, and used as a negotiation chip in the next round of strikes. After all, union films and tv shows cannot use non-union actors or crews in most cases. I imagine there will be a similar rule made that union productions cannot work with non-union vfx agencies, eventually.