PurposeThis paper aims to develop a research model that proposes a relationship among customer power, psychological empowerment and voice behavior of frontline employees (FLEs). The model also suggests that managerial openness, as a result of the manager–employee interface, contributes by mediating the effect of customer power on psychological empowerment. As a result of the job characteristic–employee interface, task interdependence is suggested as a moderator in the relationship between psychological empowerment and voice behavior.Design/methodology/approachTo analyze the data, a confirmatory factor analysis and structural equation modeling procedure using LISREL 8.5 were used. Next, the conditional process modeling was fitted to test the moderated mediation hypotheses. In this stage, the mediating role of psychological empowerment and the moderating effect of task interdependence voice behavior were tested with bootstrapping methods.FindingsThe results showed a significant relationship between customer power and FLEs’ voice behavior, establishing psychological empowerment as an intervening mechanism. Thus, customer power can be a signal of appreciation for passive and job uncontrollability to service employees. The findings also suggested the mediating role of managerial openness, which delivered a negative effect of customer power on the FLEs’ psychological empowerment. Task interdependence enhanced the link between psychological empowerment and voice behavior.Research limitations/implicationsThe specific service sector chosen for this study was retail banks. Furthermore, the study was undertaken among the FLEs of banks in South Korea. Having FLEs self-report on managerial openness raises a general concern that those employees with little experience may not have fully understood whether a manager’s current behaviors are open-minded and empowering. Lastly, the perceptions of customer power, psychological empowerment, managerial openness, task interdependence and voice behavior that all came from FLEs naturally raises concerns about the influence of method bias in these results.Practical implicationsThe significant negative and indirect relationship observed between the perception of customer power and employees’ voice through managerial openness and employees’ psychological empowerment suggested that the double deviation effect of customer power on employees’ psychological empowerment through the interface between customer and employee (customer power) and manager and employee (managerial openness). This study provides insight into the management of service customer–employee and manager–employee interactions to encourage employee psychological empowerment.Originality/valueThe main emphasis of the model is on the so-called voice behaviors that FLEs exhibit as an overall consequence of various service employee interfaces. The management of FLEs has been extensively discussed in the services marketing literature. However, few research studies have attempted to link and combine the effect of various interfaces to which employees are exposed on employees’ voice behavior. In this study, three interfaces that the FLEs are always exposed to were examined simultaneously: that of the employee and the customer (perceived customer power), the interface of the employee and the manager (managerial openness) and that of the employee and his or her job characteristic (task interdependence).