This is so obviously the right answer, I can’t believe its not upvoted more. To be clear, I stand with the union on the principal of their argument. However, the principals of economics itself, much like gravity, do not care about the nobility of your cause.
It seems to me that what the union is asking for is that the corporation act more like a benevolent force than one that is restricted by market pressures. Of course, you could use the power of government as one poster mentioned to force this issue, but those violent delights have violent ends.