[hackeraccount]

If you add value and management threatens you it's both wrong and a mistake on their part - in that it goes against managements interest.

If the Union does the same thing it's wrong - because threatening people is wrong - but not actually against their interests because as you say a Union isn't interested in the company doing well. All the company does is exploit them and the customers. The Union just wants to make sure they get a pound of flesh out of the company (and presumably the customers too).