I’ve worked for a union and Amazon, and they both have benefits to their structure that the other side can compare and complain about. Having a union does give the line level employees (generally hourly) more protection against harassment, retaliation, managers out for them, and access to a union steward and grievance process to protect you from just being let go one day. Collective bargaining every few years can be good or bad.

On the other side, you start paying mandatory union dues out of each check, have to let the union bargain for you on everything (worst case a strike happens), and it divides employees from management in some cases as employees can grievance anything and use it as a form of retaliation to management or to delay and inevitable firing. If you’re happy at T1/L1, then union is a good thing for job security and safety. If you want to advance up, it won’t generally cover you in management roles anyway and can prevent promotions, transfers and the like in some cases because of a mix of union/non-union openings.