These are _managers_. Management is not part of a union. They were presumably fired for failing to produce the company's desired result (an anti-union vote).
And or the fact they couldn't win over their workers is a sign to higher ups that they weren't good managers.
If only there was some kind of institution to help protect workers in this situation...
Napoleon was said to execute a general every now and then "pour encourager les autres" -- to encourage the others.
In the Land of The Free, one is not free to join a union. How this came to be?
Something something private companies can do what they want...
Build your own Amazon...
Freedom works both ways.
They were free to join the union.
Amazon was free to fire them.
Just like behind the iron curtain. People were free to share opinions. The party was free to send them to gulags.