Collective action is a powerful force driving social change but often sparks contention about what actions are acceptable means to effect social change. We investigated double standards in judging collective action—that is, whether observers judge the same protest actions to be more acceptable depending on who the protesters are and what they are protesting. In two studies, we used item response theory to develop an instrument of 25 controversial protest actions to measure where people draw the line between acceptable and unacceptable forms of collective action. In three preregistered experiments (N = 2,776), we found no consistent evidence for ingroup bias in terms of social class when judging protests for workers’ rights (Experiment 1), in terms of race when judging protests for and against defunding the police (Experiment 2), and in terms of gender when judging protests for and against restricting abortion (Experiment 3). Instead, we found that progressive participants (Experiments 1–3) who rejected system-justifying beliefs (Experiments 1 and 2) considered the same protest actions more acceptable when a cause aligned with their ideological orientation (for workers’ rights, for defunding the police, against restricting abortion) than when it did not (against defunding the police, for restricting abortion). Conservative participants considered the same actions somewhat more acceptable when protesters supported, rather than opposed, restricting abortion (Experiment 3) but considered all protest actions, for and against defunding the police, equally unacceptable (Experiment 2). Our findings have theoretical and practical implications for understanding the often-divided response to social movements.