Western powers often turn to international sanctions in order to exert pressure on incumbent governments and signal their support for the opposition. Yet whether, and through what mechanisms, sanctions trigger protest remains unclear. We argue that sanction threats work as an international stamp of approval for would-be protesters; they encourage collective action against governments. Moreover, sanction threats send particularly clear and coherent signals if multiple senders issue them and if they focus on human rights, which makes such sanctions threats more effective in sparking social unrest. Using count models of protest activity, we find strong support for our arguments. We corroborate our findings with qualitative evidence from the case of Zimbabwe.