In other cases, they just kick your company out.
Oh, and you can't bring anything in during setup, if it can't be carried under your arm. Seriously. For "safety reasons".
However to be fair, Hollywood is a private enterprise so it’s what the market allows — but when it comes to public money, it’s infuriating for such egregious waste and inefficiency.
We once needed to hang a network rack in our building. It was on the unions work list for 6 months. We finally just did it, a grievance was filed, and the company was fined for having a non-union person do a union job.
This was sadly the norm at that job. But it wasn't anything too exciting - nice guys, too much work to do, company wouldn't get more of them.
By contrast, European elites settled into a power sharing arrangement with unions long ago, at the end of the 19th century.
Because there's less conflict over power in Europe, there's less tension between unions and business. But because even at the height of their power (circa 1930s) unions were perpetually under siege in the U.S. by business and political interests, American unions are constantly fighting just to exist.
In the past few decades, as American unions face extinction in the private labor market, they're literally left fighting for survival. This manifests in a lot of defensiveness--i.e. the conference workers, Hollywood workers. Even in places where they're seemingly secure, they don't feel secure, and in truth aren't actually very secure. Even the most liberal, union friendly corporation or municipality has trouble resisting the pursuit of cost savings through automation and out-sourcing.
In some places unions have literally pivoted to selling themselves as jobs programs. Some government worker unions and contractor unions are in many respects a tool for wealth redistribution. In some cities and states politicians and policy makers will openly tell you that, e.g., the point of having so many unionized workers manage a conference hall is simply to provide stable jobs--jobs to gainfully employ people that might otherwise stand on the corner all day, jobs that pay enough to support a solidly working- or middle-class family.
In other words, these unions are doing precisely what so many conservatives claim the country should be doing with entitlement reform--predicate it on working. But assuming it's not just an insincere excuse, the reality is that you literally need to manufacture and distribute work in ways that are at odds with a meritocratic and especially market-driven model. Unions are literally structured to distribute work and maximize employment, which means they're a better mechanism to distribute social payments in exchange for nominal labor. Even back in the days when corrupt union leadership siphoned wealth, the disparity between leadership and wage workers wasn't nearly as great as in private business. That's especially the case today, as union financing is much more heavily regulated while, conversely, in the private labor market shareholders and managers have substantially increased their share of the profits.
Of course, these social arrangements create weird incentives for inefficiency and corruption, especially when they're as informal and ad hoc as in the U.S.
Not the idea of unions, just how the US ones turn out: a mountain of political corruption, inefficiency, and organized crime motivating an entrenched and self-perpetuating attitude. Big unions are more about their benefit than about their members, here.