Many important social and policy decisions are made by small groups of people (e.g., juries, college admissions officers, or corporate boards) with the hope that a collective process will yield better and fairer decisions. In many instances, it is possible for these groups to fail to reach a decision by not garnering a minimum number of votes (e.g., hung juries). Our research finds that pivotal voters vote to avoid such decision failure—voters who can “tip” their group into a punishment decision will be more likely to do so. This effect is distinct from well-known social pressures to simply conform with others or reach unanimity. Using observational data from Louisiana court cases, we find a sharp discontinuity in juries’ voting decisions at the threshold between indecision and conviction (Study 1). In a third-party punishment paradigm, pivotal voters were more likely to vote to punish a target than nonpivotal voters, even when holding social information constant (Study 2), and adopted harsher views about the target's deservingness of punishment (Study 3). Using vignettes, we find that pivotal voters are judged to be differentially responsible for the outcomes of their votes—those who “block” the group from reaching a punishment decision are deemed more responsible for the outcome than those who “fall in line” (Study 4). These findings provide insight into how we might improve group decision-making environments to ensure that their outcomes accurately reflect group members’ actual beliefs and not the influence of social pressures.