Let's flip the scenario. Someone comes to you and pays you to borrow your sewing machine. Then by your logic, you should not have any say in what they do with the sewing machine. It seems you are claiming that if A pays B, then A has complete say in what happens.

From a third party perspective, this is just weird. Society sees two people associating, one providing labor, that other capital, no matter how money is flowing within the association. Weirdly enough our system only allows capital owners to have any say in the running of the system (via shares and the board). Within this system, unions are one way in which the owners of labor get a say in the running of the corporation.