The US approach is more than that, for instance if every employee in a business pushes for a contract that says workers will negotiate as a block and pay new union dues, and the contract says new hires will be bound by that too, that's illegal in many states. Not just the normal "right-to-work" restrictions, the contract isn't valid even if unanimously agreed on by every current employee (union security agreements). But for shareholders they all set it up like that, with votes weighted by dollars. A new shareholder can't buy someone's shares and government says it's illegal for him to be bound by the voting structure.

And secondary strikes are also illegal in the US under Taft-Hartley.