I disagree with voting to close in this particular case - even though the question was originally formulated as being about a specific company, the question isn't opinion-based at all - there's an unequivocally correct answer in this case.
I do think that the edit helps, though, since this reflects an issue that isn't just about Amazon in particular; that being said, I personally would have just suggested the edit in the first place instead of voting to close (since that's a very easy "fix"). Editing is better than voting to close where possible.
If this really was a question specifically about Amazon, it would be off-topic and opinion-based. To quote this classic MSO post on customer support questions,
Why can't I ask customer service-related questions?
Because we don't know the answer.
Oh sure, there might be some intrepid soul who has sailed these waters before, and come out alive. They might even be able to offer some insight. There might even be the occasional employee wandering these hallowed halls. But here's the problem:
We're not Google, Facebook, Microsoft, or Apple Customer Service.
We don't set policy for these companies. We don't have telephone lines, confirmation code generators, or any authority to make decisions on your behalf. We don't track changes to policy, except by anecdote and hearsay, so any answer we give you today is going to be wrong tomorrow, if it isn't already wrong.
In general, then, the problem with company-specific regulation questions is the fact that we simply don't know the answer, we can only speculate. Also, such questions tend to be too localized (i.e. only useful to people who work for a specific company at a specific time). Finally, as the linked article goes on to explain, it really isn't our job to answer questions that the companies in question should be answering themselves.
That being said: none of the above apply in this case. It's applicable to any U.S. company where workers are considering unionizing, and we do know the answer (the accepted answer is demonstrably factually correct), and it's really not a question that Amazon should answer themselves.