They make union dues seem like a big deal, but not unionizing will cost you even more. A union will pay for itself when they negotiate a raise.
You have much fewer guarantees on pay, benefits, and work rules without a union on your side. Amazon can, and does, change policies at will. A union keeps them in check.
Bringing complaints directly to your supervisor or manager will solve nothing, and in the process, it will get you on their shit list. Sometimes, anonymity is priceless.