["Journal of Organizational Behavior, EarlyView. ", "\nABSTRACT\nWhy do employees conceal their coworkers' unethical behavior and who is most likely to do so? To address these questions, we begin by developing and validating a psychometrically robust measure of relational cover‐up behavior (Study 1). Using a two‐wave study (N = 475), we then test the argument that employees may experience an identity threat in response to witnessing a coworker engaging in unethical behavior, which can motivate employees to cover up the coworker's unethical behavior, especially when they closely identify with the coworker (Study 2). Theoretical implications include identifying the process through which relational cover‐up behaviors can emerge, when they are especially likely to do so, and the detrimental consequences of coworker identification for relational cover‐up behavior. Our research also provides the methodological foundation for scholars to empirically study relational cover‐up behaviors, while offering practical guidance to manage these pervasive and damaging behaviors.\n"]