You might not want to hear it, but those that were fired recently were using their company email address to organize union discussions. You just can’t do that, no matter how justified one is to pursue unionizing.
> Also, restrictions on your efforts to communicate with co-workers cannot be discriminatory. For example, your employer cannot prohibit you from talking about the union during working time if it permits you to talk about other non-work-related matters during working time.
I worked at a place where all emails had to be work related.
That was in the Cable TV Industry. Which, in it's own way makes sense; that industry has a 'Owner'->'Prime Contractor'->'Subcontractor' tiered setup for work that has always had the unspoken purpose of preventing field workers and installers from unionizing.
Wanted to send out an email about a fundraiser or special weekend craft thing? Had to have HR give the OK.
-IF- Amazon had and enforced such a policy it could be considered non-discriminatory. But I'm somehow doubting such a policy is fully enforced even if it is on the books.
(This was in the UK.)