The article is divided into two parts. The first describes Hayek's critique of the progressive tax system since its conception of social order and fiscal rationality. Hayek thinks about a key principle in liberal democracies: majority rule. And stretching comments to the influence of morality in taxation decisions. The second is aimed at analyzing the reception of Hayek in constitutional economics Brennan and Buchanan. However, in the interpretation of tax policy has decisively if governments reflect a tyrant or benevolent Leviathan State. The Fiscal Constitution must be accompanied by a monetary constitution. Both constitutional forms are related and prevent leviathánico power of governments, especially when they are short stay. Although, for the authors, the Fiscal Constitution has important implications for monetary constitution.