Depending on what it was. I may confront the boss about it.
Call the ethics hotline
I would pull him or her to side a.nd tell them that I didn't think they should be doing that and then if that didn't work go a step above them
Speak to someone higher them or report it to government agency
File a formal complaint!
Report your boss to HR after sending yourself an email documenting the event and how you felt about it.
Talk to your boss about how "some people" might not appreciate his actions if it became common knowledge.
Speak to HR.
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