> Under the NLRA, it is illegal for your employer to:
> Fire, demote, or transfer you, or reduce your hours or change your shift, or otherwise take adverse action against you, or threaten to take any of these actions, because you join or support a union, or because you engage in concerted activity for mutual aid and protection, or because you choose not to engage in any such activity.
You can get a basic overview of this topic by googling things like NLRA, NLRB, and protected concerted activity, including very recent examples of how these concepts have applied. They're much broader protections than you think, and Amazon has very clearly broken them. That's why their spokesman is giving out contradictory statements like saying that they allow employees to discuss eachother's working conditions, then firing them for exactly that.
Do not fall into the trap of thinking that "the company has a policy" or "at-will employment" means "you have no legal rights".