This happened to me recently where I had to make a judgement call about pursuing legal action and chose not to. It was regarding being reprimanded for discussing my salary with coworkers (with a heavy implication that I would be fired if I didn't stop).

Looked into it a bit. Discovered it was illegal under US law, but as far as I could tell the best case scenario is that they would be required to re-hire me in the event of termination and possibly give me back pay.

I sent an email to all my coworkers explaining what had happened and listed the phone number for the nearest regional NLRB office. Then I quit.

Still have some doubts about that decision. The company culture had made me to feel like I was doing something shameful either way so my emotions were a little all over the place at the time. I'd had a little more resolve I might have "played it smart" instead of blowing things up but the company was honestly too much of a juggernaut to be remotely effected by any action I took.

To be fair I should have documented each of those occurrences knowing that such communications were improper and I didn't.

Also, it wasn't the company that failed in this regard. It was specifically the manager. Without evidence either way though clearly a conflict had occurred and HR would have to make some determination. If I were in the position of HR I would have educated the manager on the proper way to administrate their concerns to cover the company, which is what I suspect happened.

Since leave, disability, and discrimination in general are hard to prove for all parties involved typically the biggest threat isn't immediate legal consequences. More concerning is reputational harm should something like that could be exposed. Many large companies offload managing these responsibilities unto external contracting vendors to ensure both the company is entirely insulated from malfeasance and the employee is fully protected.