The purpose of this study is to understand the important role that organizational citizenship behavior (OCB) of contact employees plays in customers' evaluations of service quality. To this end, this study examines how organizational citizenship behavior displayed by employees at service encounters affects customer-perceived service quality, and also investigates the antecedents of organizational citizenship behavior from a social exchange theory perspective through employees' job satisfaction and trust in supervisors. In this study, which simultaneously considered both customer and contact employee data, the hypothetical model demonstrated a level of model fit that, while not entirely satisfactory, was at least acceptable. All three proposed hypotheses were supported in both the model accounting for common method bias and the model not accounting for it. Furthermore, unlike prior research, when overall organizational citizenship behavior was classified into three more specific types of OCB, the path estimates between these types and their antecedents were found to be non-equivalent based on chi-square difference tests. However, the degree of influence that these three types of organizational citizenship behavior exerted on service quality was found to be equivalent.