Originally from the Netherlands, unions are often organized industry-wide. Unions are not organized via a single business because that is dumb. Unions are there to support the workers, all workers, so it makes sense to negotiate industry-wide, for instance per State or important and clearly marked geographical area.
What is also the case is that there are multiple unions to choose from (three different nationally-operating unions). There is competition among unions, and when one union overcharges its members and ends up spending lots of money on their own personnel, then there are alternatives. Workers can pick from different unions.
Naturally, these unions do all end up around the industry-wide negotiation tables with industry-wide business representatives.
Everyone knows that being divided is automatically a weak point, so organizing oneself inside just one business can indeed lead to being played out. Unions must organize themselves industry-wide in sensible geographical areas. Competition has to be included among unions nevertheless because their real boss is the worker, and the worker must have a choice so the unions cannot just sit on their butts and play friends with the companies or milk the situation. Competition is good, not just among businesses but also among unions.
The setup in the USA of businesses, unions, and the half-democratic voting system we have here means that workers have to be smarter than they are today. Industry-wide negotiations is the only way to get rid of jobs that do not pay livable wages. We can rise as a nation for us all. Competition is the only way to make unions pay real attention to whom they serve.