We test the effect of inequality on peer punishment in a common-pool resource (CPR) experiment with equal endowments (Equal) or unequal endowments (Unequal). Peer punishment reduces extractions in both treatments, but it is more effective in Unequal. Subjects with lower endowments coordinated around an Equal Earnings norm, subjects with higher endowments matched, and peer punishment tightened this coordinate-and-match dynamic. By contrast, there was less coordination in Equal, and as a result, more peer punishment and lower payoffs.