We argue that individuals have general responsibility attribution heuristics that apply to collective decisions made, for example, by families, teams within firms, boards in international organisations or coalition governments. We conduct laboratory and online survey experiments designed to tease out the heuristics subjects use in their responsibility attribution for collective decision makers. The lab experiments comprise a collective dictator game with weighted voting power of the decision makers and a punishment possibility for the recipients. Our results show that recipients punish unfair allocations and mainly target the decision maker with proposal power and with the largest vote share. We find rather weak evidence that decision makers with veto power are targeted or that recipients engage in punishment proportional to weighted voting power. The survey experiment tests whether subjects indeed believe that the decision maker with proposal power has the most influence on the collective decision outcome. The results confirm this conjecture. We discuss the implications of our findings for theories of vote choice in contexts of multi-party governing coalitions.