The back of the union movement in the United States was pretty much broken when Ronald Reagan broke an air traffic controllers strike by firing 11,359 of them and replacing them with members of the military. He also imposed a lifetime ban on rehiring any striking worker. Then they decertified the union. Sent a message.

Their justification for this was that the strike was illegal, after Reagan himself declared it illegal via an executive order.

https://www.politico.com/story/2017/08/05/reagan-fires-11-00...