I worked at a union retail job for three years and saw the pros and cons firsthand.
We had a problem employee who was untouchable regardless if he was completing his job duties (assuming he showed up at all). Eventually this came to a head as he would spend 30min+ in the restroom. To address this they instituted a “log all bathroom breaks” policy _for everyone_ which caused the employee to not show up again.
However, the company kept the policy in place for weeks until I sent a strongly worded email to the union rep (who was unaware he was overseeing our store). He made a visit the next day and the policy was promptly changed.
So while I was glad to have a Union to override such policies I do wonder if the problem employee would have been around for so long without it.