Dense in-group and scarce out-group relations (network segregation) often support the emergence of conflicts between groups. A key underlying mechanism is social control that helps to overcome the collective action problem within groups, but contributes to harmful conflicts among them in segregated settings. In this study, a new experimental design is introduced to test whether internalized social control affects contribution decisions in intergroup-related collective action. Subjects played single-shot Intergroup Public Good games in two groups of five each without communication. Subjects were connected via computers and connection patterns were manipulated to detect forms of social control that are activated conditional on expectations and on the composition of the artificially created ego-network. Results confirm the influence of behavioral confirmation and the conditional impact of internalized traitor and selective incentives. As an aggregated consequence of these social control effects, harmful intergroup outcomes were least likely when members of the groups were arranged in a mixed network. JEL classification: C91; C92; D74; H41; Z13