People can experience great distress when a group to which they belong (in-group) is perceived to have committed an immoral act. We hypothesised that people would direct hostility toward a transgressing in-group whose actions threaten their self-image and evoke collective shame. Consistent with this theorising, three studies found that reminders of in-group transgression provoked several expressions of in-group-directed hostility, including in-group-directed hostile emotion (Studies 1 and 2), in-group-directed derogation (Study 2), and in-group-directed punishment (Study 3). Across studies, collective shame-but not the related group-based emotion collective guilt-mediated the relationship between in-group transgression and in-group-directed hostility. Implications for group-based emotion, social identity, and group behaviour are discussed.