I'm not happy about that, but what bigcorp doesn't try to bust unions? Certainly Walmart does it too, so that really seems to just be an instance of Amazon merely matching their competitors' abuses.
I know it's slightly off topic, but in some areas of Europe it is considered essential for any big employer to have a healthy union. The employer encourages unionization, and there are certain benefits for them too.
Remember when there was a unionization vote at a Volkswagon plant in Tennessee, and VW was like, "please vote yes, we like working with unions and believe it'll make everybody's lives easier". But state and national politicians, not to mention outside lobbyists, created a huge campaign to oppose the vote? And then the "no" campaign succeeded.
You can't make this stuff up. But it drives home the reality that anti-union sentiment is strong in the U.S.; and deep. Most non-skilled workers in this country are very skeptical of unions, if not outright cynical. And it's always been this way, going back to the 19th century.
IIRC, there was a second vote at that same plant a little later. That time VW HQ just kept their mouth shut. And they loosened the leash on their American managers, who mostly opposed unionization. Obviously it failed again.