How can civil society organizations efficiently support a sustainable development of democracy and prevent a democratic breakdown ? This papers suggests that the type of the political regime is determined by the nature of power relationship between the state apparatus and the civil society. Focusing on the role of the Tunisian General Union of Labor (UGTT), I explain that both the organizational strength of civil society organizations and the government's toleration to pluralism are necessary but not sufficient conditions for democratization. The case study of Tunisia’s central union indicates that the engagement of the civil society in a continuous and progressive “war of position” with the state is a critical determinant of the regime type. The theory is built thought an analysis of archival documents and in-depth interviews conducted with current and former leaders and rank-and-file members of the UGTT, as well as political actors who interacted with the union since Bourguiba’s rule. While the strong organizational structure of the union didn’t see any significant change since the 1950s, its willingness to cooperate with the hegemonic political parties of Bourguiba and Ben Ali regimes prevented it from exploiting multiple historical opportunity of political openness to advance democracy. In contrast, the combination of both strategic and tactical decisions taken by both the UGTT and the governing elite since the fall of Ben Ali regime in 2011 placed the Tunisian civil society in a posture that prevented the state from using its power to halt the democratization process, and forced it to make further concessions. In addition to the adoption of a militant approach similar to the one taken against Bourguiba regime to claim its independence from the ruling party, the union worked towards the accumulation of power through the exploitation of the divisions between the weakened political party sharing state-power. It only through the sustenance of this conflictual relationship with the state apparatus that the Tunisia’s main civil society organization was able to prevent a democratic backsliding.