This article analyzes the struggles of the Catalan government to organize a referendum on secession and the constitutional framework invoked by the Spanish central authorities to prohibit it. The repression of secessionist referenda within the Spanish constitutional framework triggers several problematic questions concerning the role of constitutional supremacy in handling subnational secessionist challenges developed under a pacific and democratic framework. The article offers a comparison between the Spanish-Catalan case and other examples of secessionist referenda within liberal democracies, underscoring that the Spanish solution of repressing such referenda through criminal law is unique in the liberal democratic context. The article also offers a description of the political, historical, and legal circumstances surrounding the Spanish central authorities' actions that explains the Spanish constitutional response to both the Catalan Consultation held on November 9, 2014, and the referendum on Catalan independence held on October 1, 2017. The article concludes by arguing that the prohibition of the Catalan referendum initiatives on independence and their subsequent prosecution through criminal law may cripple the basic pillars of the Spanish liberal democracy designed under the 1978 Spanish Constitution.