In the face of growing global competition, unions had common challenges and difficulties in retaining their bargaining power. Yet, their responses to market restructuring varied within and across countries resulting in a variety of outcomes. This dissertation tries to answer the question of why union responses differed and why they had varied degrees of success in their attempt to influence the restructuring designs. For this, this study examines labor responses to privatization and public sector restructuring in Korean telecommunications and railways. The main findings of this dissertation can be summarized as follows: first, the changes in the political contingency increased opportunities for the Korean Railway Workers' Union (KRWU) while reducing them for the Korea Telecom Trade Union (KTTU). Due to this difference in the extent of political opportunities, KTTU was constrained to take a defensive position whereas KRWU escalated its militancy. In the Korean institutional context where both unions were deprived of institutional access, the increase in political opportunities tended to increase labor militancy for KRWU while the reduction of the latter contributed to the restraint of militancy for KTTU. Second, the persistent replacement threat of the leftist faction sustained the leadership inclination towards militancy at KRWU while the waning of such a threat reduced the incentives for militancy for the KTTU leadership. Third, in regards to strategic effectiveness, KRWU was more successful in obtaining concessions from government/management than KTTU. Such variation can be explained by a greater strategic ability of KRWU leadership in mobilizing membership and socio-political resources. Findings contribute to the current debate on national models theories. Unlike the expectation that non-coordinated industrial relations polity would be associated with market-driven unilateral restructuring, this dissertation argues that there exists a subnational variation in restructuring outcomes related to the differences in the strategic capability of unions. This led to questioning the uniformity of national models. Instead, this dissertation found the central role played by the strategic choices of labor unions in creating within-country variations in the restructuring outcomes.