Full disclosure: I've always been anti-union for my own personal approach to life. I do see the value in unions, I've just always, to this point, been a go-it-alone-and-fight-my-own-battles kind of person. I don't want to be beholden to a union or their rules any more than I want to be beholden to an employer beyond my contractual obligations for which I'm paid.
That said, people should take note of what happened when Walmart used these tactics. Employees then went on to suffer such things as zero hour contracts, contracts where time was just shy of the legal requirement to give them benefits, pay was no more than the minimum required in any given state/province and people became slaves to their jobs because they couldn't afford the time off to find other jobs because then they wouldn't be able to make ends meet or there were no other jobs so Walmart had zero incentive to pay any more than absolutely required to by law. etc. etc. etc. because humanity is only afforded if legally required [which I personally find disgusting].
These are tactics to prevent a coalition of employees from having their rights heard and maintained... even with this coalition someone is fighting to maintain and win your rights(!!!!!) There's something very wrong with anyone having to fight for their rights to be given, but that's another discussion. In a commercial environment that allow employers to behave this way, where the only advantage to winning your rights is in a coalition of the workforce holding employers to account, unions absolutely must not only be allowed but must also be protected.
Its okay if you're bullheaded enough or within your means enough to walk away if your rights aren't given fair consideration and honoured, but if you're in a position where you're a prisoner to your job, i.e. can't afford to take time off to find another job/other income, or there are no other jobs in your area and you don't have the means to leave etc. you don't have any bargaining chip.
No employer should ever have the privilege of keeping you prisoner, nor preventing you from having a means to bargain for your very right to fair treatment.
Amazon needs to be severely reprimanded for this and taught a lesson about what it means to honour employees' rights.