In 2016, the Government of Juan Manuel Santos and the Revolutionary Armed Forces of Colombia (FARC) signed an important Peace Agreement that would end an armed conflict of more than 50 years. This Agreement to be implemented needs a legal regulation that will need to go through the legislative vote to have legal certainty. This was done under the Fast track or fast track mechanism, which reduces the common times of legislative procedures, with the aim of having speed and maintaining the stability of the pact. Voting to approve said regulation began with the common legislative behavior of the said Government: its bench was majority and there was a cohesive opposition bench but whose legislative capacity was lower. In the middle of the voting period, the Democratic Center Party, the only party declared in opposition to the Government, demanded the Legislative Act for Peace before the Constitutional Court and ruled in its favor by changing the rules of the game and the mechanism of 'Fast Track '. From that moment, lawmakers began voting differently than they had done during the legislature. Therefore, this study aims to analyze the legislative behavior in the Congress of the National Unity parties and the opposition to the government of Juan Manuel Santos in the voting of the projects for the implementation of the Peace Agreement before and after the Judgment.