We explore the formation of coalitions to provide a public good when some players are averse to payoff inequality between coalition members and non-members. A model is presented to demonstrate how inequality-averse preferences could cause players to deliberately block profitable but inequitable coalitions from forming, and how the likelihood of such blocks is affected by the magnitude of payoff inequality. We then empirically examine coalition formation rates using laboratory experiments. Our results show that profitable coalitions are less likely to form the bigger the gap in payoffs between members and free-riding non-members. The experimental design allows us to tease out potentially confounding effects between the level of inequality and the minimum number of players required to make the coalition profitable. As predicted, controlling for the size of the participation threshold, we find that coalition formation rates fall as the payoff gap between members and non-members is increased.