If my boss asks me to do something, and I refuse, what do you imagine will happen? I will get fired for insubordination. It's pretty easy to get people onboard if their paycheck depends on it.
You'd need to have this specific request from supervisor on paper, with witnesses, all video recorded with supervisor's consent. Otherwise you'd be sued into poverty for besmirching.
When the supervisor fires you, for such a reason, it seemed to be important enough. You also don't need any proof to report someone to the authorities.
Even if the the company has enough lawyers to win in court, it is still expensive. That's why the lawyers are among the risk aversest. So reporting to a company internal lawyer might already be enough.
