>They can do that even with a union. The difference with a union is that they can collectively stop working if the employer violated a clause like "union member

>They can do that even with a union. The difference with a union is that they can collectively stop working if the employer violated a clause like "union members must be fired with reasoning pre-approved by the union", and then the employer either needs to find new employees for every person that was in the union or needs to re-negotiate terms with the union, likely including reparations ie. re-hiring the coworker. But that potential response by the union should be enough of an incentive that casually firing somebody over Zoom for no reason is removed from the employer's SOP.