Nowadays, manufacturing companies are looking to improve their sustainability in the market. However, there are several factors that negatively affect it, such as workload imbalance among workers, defective parts, and customer complaints, to name a few. This paper presents a case study of a workload imbalance in a global customer complaint follow-up process in a manufacturing company, generating lagged complaints (no follow-up), which has negatively impacted the sustainability of the process. Due to this, the objective of this project is to increase the sustainability of the process by reducing the number of delayed complaints. To do this, the causes of the problem are identified. Then, an analysis of the process flow map is performed to see the current distribution of the workload among the different plants of the company. Moreover, corrective actions are implemented and followed up. Subsequently, the process is standardized, transferred by parts to the different plants, monitored for control, and the effectiveness of the actions is measured. As a result, there was an increasing trend in terms of compliance in the capture of complaints, starting with 84% and reaching 97%. Similarly, the total number of complaints received showed a decreasing trend. Finally, zero delayed/indefinite complaints (no follow-up) were obtained. Therefore, it is concluded that workload balancing has a positive impact on the sustainability of processes in manufacturing companies.