Genuine question because I am very curious about worker unions in the USA vs worker unions in The Netherlands (and many other countries I imagine):
From what I read on Reddit and other social media about workers trying to unionize (some more successful than others), it seems that workers for employer X need to start a union consisting only of workers for that employer. In The Netherlands (and again – I imagine many other countries) we have many independent worker unions for many lines of work, of which you can become a member by just subscribing (and paying a membership fee of course). Even if your particular employer doesn't have a union itself.
So my question is this: what is to stop anyone or a group of people from starting an independent worker union for, say, retail workers in general? Does it have to be linked to a specific employer?
EDIT: I can't seem to edit the title, but by “global” I meant to say “generic” or “nationwide”.