This is absolutely true. My former employer (a big box retail company) reduced my pay while I was on holiday. I had been there for years and accrued a bunch of pay rises - but the company got bought out and the new owners thought they could strip me of these because they felt they were temporary and non-contractual.
I got some legal advice that basically said they can’t do that sort of thing and had a meeting scheduled with HR. I went in with my notepad, I stayed calm - pleasent even - no angry shouting or slamming tables with fists, I just politely asked them questions and wrote down everything they said, then read their answers back to them to confirm thats what they said. I had about 6 questions prepared and by the 4th they were visibly uncomfortable, it was an amazing feeling making them squirm like that. After I got done asking my questions, I dropped the legal advice I had been given on them and it was obvious the answers they gave supported my case very heavily. They panicked and reversed all there decesion plus I got back-pay.
But if the first thing I had done is charge in making accusations and quoting the law I know nothing constructive would have happened.
See the goal is to bury them in their own words.
Edit: predictably the company went bust the next year. So long Office Outlet!