When international institutions obligate their members to impose economic sanctions against a target state, how much do those sanctions obligations actually impact their members' behavior? To date, the consensus view has treated all international institutions as if they are equally capable of making multilateral sanctioning efforts more effective. Building upon the enforcement theory of sanctions cooperation, we instead theorize that the ability of international institutions to constrain their members from engaging in spoiler behaviors degrades the larger they are. We hypothesize that sanctions obligations imposed by smaller-sized institutions are more effective at preventing their members from becoming extensive trade-based sanctions busters than those imposed by larger ones. We test our hypothesis via a quantitative analysis of how the involvement of five different international institutions in sanctioning efforts influenced their members' likelihoods of sanctions-busting. We find that only the smaller-sized institutions we examine appear capable of constraining their members from undercutting sanctioning efforts. Notably, we find no evidence that the United Nations' sanctions actually prevent its members from sanctions-busting.