I think the main question here is balance. We could have the same argument with pretty much everything - not only companies / unions. In the end each party is

I think the main question here is balance. We could have the same argument with pretty much everything - not only companies / unions. In the end each party is motivated to use its own power to optimize for their end. Systems like markets only seek equilibrium if there is a balance in power between parties. Balance needs to be a neutral position that's still beneficial (read fair) for all sides.