The study develops and examines the relationships among relational norm, supervisors’ and subordinates’ social undermining and fear of retaliation that explains how and when relational norm is associated with social undermining. Data were collected from 120 full time employees and their coworkers respectively. The results from examining a moderated-mediation model reveal: (1) relational norm negatively relates to supervisors’ social undermining; (2) supervisors’ social undermining positively relates to subordinates’ social undermining; (3) the strength of indirect relationship between relational norm and subordinates’ social undermining via supervisors’ social undermining is negative and stronger (weaker) when subordinates’ fear of retaliation is high (low). The study discusses the theoretical and practical implications and provides some suggestions for the future study.