This study explores the psychological mechanism underlying and the boundary conditions affecting the relationship between managers’ unethical pro-organizational behavior (UPB) and subordinates’ willingness to engage in UPB. Drawing upon social learning and social cognitive theories, employee moral disengagement was predicted to mediate the relationship between managers’ UPB and employees’ UPB willingness; in addition, the moderating roles of both leader–member exchange and ethical relativism were investigated within this relationship. The results, based on 29 managers and 200 subordinates in Vietnam, supported the proposed mediation model. The findings further indicated that leader–member exchange augmented the positive relationship between managers’ UPB and employee moral disengagement, whereas employee ethical relativism weakened the positive relationship between moral disengagement and employees’ UPB willingness. By elucidating the underlying mechanism and boundary conditions, our findings offer an empirical basis for considering managers’ UPB as a critical antecedent to employees’ willingness to engage in UPB and also inform effective intervention approaches for organizations to constrain UPB.