Retaliation against whistleblowers is a well-recognized problem, yet there is little explanation for why uninvolved peers choose to retaliate through ostracism. We conduct two experiments in which participants take the role of a peer third-party observer of theft and subsequent whistleblowing. We manipulate injunctive norms and descriptive norms. Both experiments support the core of our theoretical model, based on social intuitionist theory, such that moral judgments of the acts of wrongdoing and whistleblowing influence the perceived likeability of each actor and (...) ultimately influence intention to ostracize each actor and indicate more willingness to ostracize the whistleblower than the wrongdoer. When we vary norms for the wrongdoing in Experiment 1, we find that descriptive and injunctive norms indirectly influence intentions to ostracize both the wrongdoer and whistleblower. These relationships are serially mediated by the observers’ moral judgments of the act and likeability of the actor. When we vary norms for whistleblowing in Experiment 2, the injunctive norm manipulation affected moral judgment of the action of whistleblowing, and we do not observe any other significant effects of the norm manipulations on moral judgments of the actions of wrongdoing or whistleblowing. (shrink)