20 October 2016The effects from voluntarily choosing to accept or reject solidarity with outgroup members oningroup cooperation has not been studied from a behavioral perspective yet. Our contribution to theliterature on intergroup solidarity and ingroup cooperation is twofold. First, building on the publicgoods game, we design a novel experiment that allows us to study intergroup solidarity by allowinghigher endowed groups to voluntarily share the benefits from their group account with less endowedgroups. Second, we show that voluntarily – by voting – refusing solidarity with a less endowed groupresults in a breakdown in cooperation within the group that voted. The mere thought that sharing withoutgroups is costly spills over to the ingroup contribution decisions