Comment by mindslight

For an example of how unions can get involved in unexpected ways, take a look at the SAG releases for participating in hobby projects (eg 48 Hour Film Festival). It's just an additional piece of paperwork, but it does demonstrate a dynamic that the union has a legitimate interest in overseeing and could just as well prohibit. A software union would surely become involved in bootstrapped startups, hackathons, and work on Free software. It's possible for these areas to be treated intelligently by a union, but it's also possible they wouldn't be.