CWA, CAA, CERCLA, and RCRA provide these protections for whistleblowers and a framework for financial incentives, though these incentives are paltry compared to SEC whistleblower rewards.
I've seen it happen, or what probably was retaliation, but how do I know for sure? They said the person wasn't competent or doing their job when they got fired. I don't know for sure if that was true, but I do know they reported significant theft that would likely have involved someone higher up, and not long afterwards he was fired.
I find it obvious that such retaliation happens, otherwise it would be strange to have such laws.