We provide a model and experimental evidence on the effects of non-monetary punishment (NMP) by peers among communities of Uruguayan fishers exploiting a common pool resource (CPR). We find a) experimental groups composed of fishers from different communities (out-groups) who are sometimes in conflict over fishing territories did not overexploit the resource more than groups from a single community (in-groups) and, unlike in-groups, out-groups reduced their exploitation of the resource in response to the threat of punishment; b) cooperative individuals punished free riders while a substantial amount of punishment was targeted by free riders on cooperators, who [in turn] responded by increasing their exploitation of the resource; and c) wealthier individuals practiced greater overexploitation of the resource. Our results suggest that the relevance of in-group favoritism in promoting cooperation due to social preferences may be overrated, and that the effectiveness of peer punishment is greater when individuals are motivated by social preferences and also that coordination is required to prevent anti-social targeting and to enhance the social signal conveyed by the punishment.