I am watching this with great interest. Especially if the vote passes, would amazon just pull out of the area all together. (similar to walmart's strategy)
Both the threat and reality are fairly well-established to be unlawful, though the penalties are mild enough that the threat is very common and follow-through is not uncommon.
A Canadian precedent for the action of closing the newly unionized store. Not a legal precedent for the US, of course.
https://www.nlrb.gov/about-nlrb/rights-we-protect/your-right...
https://www.epi.org/publication/unlawful-employer-opposition...
That's the defacto play, but, given that Biden is known to be quite pro-union, shutting down the warehouse might well have unintended consequences for Bezos.