Employees are often driven to speak up by intense emotions such as frustration, anger, and dissatisfaction. Yet the very emotions that spur employees to express voice may compromise their ability to express it constructively, preventing managers from reacting favorably. I propose that to speak up frequently and constructively, employees need knowledge about effective strategies for managing emotions. Building on theories of emotion regulation, I develop a theoretical model that explains the role of managing emotions in the incidence and outcomes of voice. In a field study at a healthcare company, emotion regulation knowledge (1) predicted more frequent voice, (2) mediated by the emotional labor strategies of deep acting and surface acting, and (3) enhanced the contributions of voice to performance evaluations. These results did not generalize to helping behaviors, demonstrating the unique role of emotion regulation in challenging rather than affiliative interpersonal citizenship behaviors. This research introduces emotion regulation as a novel influence on voice and its consequences.