Perhaps the worker is at fault, but in (good) aerospace companies one person's mistake cannot lead to a bad unit going out the door. At the very least, two people need to be wrong in the same way - but more likely, several people would need to miss the problem.
That being said, "operator error" as a reason for a problem is heavily discouraged (at least in official reports). Rather, it's typical to blame a human factors issue, commonly one of the "dirty dozen" [0]. I couldn't say exactly which ones are present at Boeing but frankly, from the public reports almost all of them sound applicable. With this in mind, process change is the only appropriate remedy, regardless of what the union thinks. I've never heard any union people get mad at something that improves their job though.
That being said, "operator error" as a reason for a problem is heavily discouraged (at least in official reports). Rather, it's typical to blame a human factors issue, commonly one of the "dirty dozen" [0]. I couldn't say exactly which ones are present at Boeing but frankly, from the public reports almost all of them sound applicable. With this in mind, process change is the only appropriate remedy, regardless of what the union thinks. I've never heard any union people get mad at something that improves their job though.
[0] https://skybrary.aero/articles/human-factors-dirty-dozen