The trick is to setup a balance of power, so that the company has good reason to negotiate with the union but neither side is at the others mercy. If the company really feels that the unions demands are too much then it need to be able to replace the union employees, but at the same time companies can't be in a posistion to fire union people simply because they don't like dealing with the union.

I don't have any brilliant ideas about how to create that balance though.

Jay