Shouldn't any one of those 20 employees who wants to bargain on their own be able to?
You're adorable.
In forced unionization states, they are required to pay union access fees, if they choose to opt out of the union, whether they wish to be represented by said union or not.
In "forced unionization" states, as you so soberly and non-hackishly call them, employers and unions are allowed to set rules on that for themselves. One who doesn't like it is, as the free market über alles types are always reminding us, free to find a job elsewhere.