Who will train the replacments if you have fired all the trained workers. I don’t think there is an alternate pool of experienced unemployed longshoremen to hire from. That is a lot of experience you would give up that would take a months/years to get back to regular levels of productivity .

That’s why in the good old days you hire Pinkertons to use physical violence to intimidate and break up the unions so you can keep the workers. Much easier than replacing thousands of skilled workers