This study examines whether and how constructive voice (i.e., suggestions intended to promote positive changes at work) is contagious. Guided by social cognitive theory, we propose that witnessing a co‐worker’s voice increases an employee’s propensity to engage in voice via two parallel psychological mechanisms: voice self‐efficacy beliefs and voice instrumentality beliefs. Data collected from a vignette experiment (N = 661), an experience‐recall experiment (N = 548), and a field study (N = 549) provide evidence supporting the proposed voice contagion. The results also suggest that voice contagion is activated by witnessing the voice of any co‐worker, as the evidence supported voice contagion even when controlling for employees’ evaluations of co‐workers’ warmth and competence. Thus, this study contributes to the voice literature by identifying social learning from co‐worker voice as a crucial relational antecedent of employee voice and revealing two possible processes by which voice spreads in the workplace.