In modern manufacturing systems, maintenance operations are the key to improve machines' reliability and availability, and hence to improve system productivity and quality. Maintenance can be roughly categorized to Corrective Maintenance (CM) and Preventive Maintenance (PM). Since the production system is highly stochastic and maintenance actions could either be perfect or imperfect, it is a complex decision to make on when, where, and which type of maintenance action should be taken. In this paper, a maintenance control law is proposed to schedule cost-effective maintenance, either CM or PM, in a real-time fashion. The control cost consists of a resource cost, and the immediate and potential production losses due to the stoppage caused by the maintenance action. A data-driven model is used to evaluate the production losses. A case study is performed to demonstrate the effectiveness of the proposed control method by comparing three different maintenance policies.