Union decline and labor market dualism are common assumptions about the state and role of trade unions today. At first glance it may appear that decline also characterizes unions in South Korea. However, empirical evidences contradict this notion, including rising union density and progress in organizing precarious workers. To explain this enigma, this chapter traces the historical strategies of organizing the longest-standing and most extreme form of precarious worker, precarious construction workers. This history is marked by numerous trials and errors and strategic shifts. However, after decades of stagnation in recent years, the precarious construction workers’ union has developed its own unique and successful tactical repertoire and created a mix and virtuous circle of power resources that has resulted in significant progress in organizing workers. These successes contributed to the quantitative growth and qualitative change of the KCTU and South Korean unions in general. However, under the Yoon administration, the precarious construction workers’ union is facing new challenges and is being asked to make another strategic shift to overcome them.