One of the main arguments in favor of unions is they have contracts—that means that unilateral changes of employment policy are not permitted.
Those companies that implemented unilateral policy changes on vaccines are making the argument as to why unions exist.
I will have no sympathy for those companies if they are unionized in the future.
In a free enterprise capitalist system, every company has the right to make stupid decisions. Capitalism is self correcting. It makes stupid ones go bankrupt. But point remains, PRIVATE corporations must have the right to make any decision they want and are liable to be sued if their decisions cause hurt.