This paper examines the economic implications of the Supreme Court of Korea’s 2013 en banc decision that brought fixed bonuses and performance-based pay within the scope of ordinary wages, and conducts an empirical analysis using a robust difference-in-differences design that exploits variation in labor cost shocks as treatment intensity. Theoretically, when wage adjustment is constrained, the ruling creates dual cost pressures by increasing both overtime pay and quasi-fixed labor costs per worker. The empirical results show that, although the ruling had limited effects on hourly wages and employment, there is no evidence that labor costs per worker increased. This reflects firms’ cost-saving adjustments through the reallocation and restructuring of working hours. As a result, firms reorganized working-time arrangements, reducing total labor input in the short run and replacing overtime hours with contractual working hours in the long run. These findings suggest that the longstanding debate over the scope of ordinary wages, often framed as a zero-sum conflict between labor and management, should be reconsidered within a framework of mutual cooperation aimed at minimizing short-term costs and enhancing long-term welfare.