This paper analyzed the problem faced by a maintenance department of an Information Technology company, which recorded a huge amount of penalty cost each month. The cost is incurred when a service breakdown is solved beyond the agreed-upon duration, as distinctively stated in the Service Level Agreement established with its customers. Therefore, the objective of the paper is to present a workforce schedule model that would minimize the average total time of service in the system and maximize the total number of completed jobs. A simulation modeling was used and two alternatives of workforce schedule are compared. In comparison to the existing schedule, switching to the first alternative of Grouped-Efficiency-based Staff Schedule is expected to reduce the average total time in system of the highest severity service by 69% and increase the total number of completed jobs by 15.7%.