I just finished Sam Walton's Book "Made in America". It's about Walmart, but I heard somewhere it's required reading for all Amazon managers. Anyway, it's a fantastic book, and there's something about their Anti-Union stance in it: "I have always believed strongly that we don’t need unions at Wal-Mart. Theoretically, I understand the argument that unions try to make, that the associates need someone to represent them…
Now, the interests of the entire staff at any given Wal-Mart store are generally not aligned with those of Mr. Walton, nor are the interests of engineering staff and line managers aligned with the interests of the C-suite. Simply having supervisory authority doesn't really change the pressures on you, especially when there's an IC track (whether baker or engineer) very close to your role. Nor are the interests of the staff of any Starbucks store aligned with those of Starbucks corporate, nor those of almost everyone involved with physically shipping Amazon packages with those of Amazon corporate, nor those of the people racking Google datacenters and those of SVPs at Google, etc.
So there is an entirely natural division that already exists. Our present form of union forces everyone with supervisory authority to take the side of the big bosses. I think if we had unions that could genuinely represent all laborers, they'd work a lot better.