The best way to deal with a breach in ethics is to contact your supervisor first and then decide together what to do next.
You could confront the person but you run the risk of putting yourself in harms ways or gaining a bad reputation. It isn't your responsibility to correct the person but instead speak to your supervisor or manager and they will deal with the matter at hand. It is always important to speak up about breaches in ethics whether this is at work, school, research etc.