The local governments approve ordinances in which it is decided that certain fundamental rights are limited or optimized in attention to collective goods whose protection is within their competence. From the critical analysis of the regulatory space that the power of the Ordinance in fundamental matters occupies in praxis, it would be possible to induce some general guidelines. Based on this analysis, this work aims to formulate a canon, not only descriptive but also prescriptive, on the presuppositions, requirements and functionality of the Ordinance, according to which it is considered a "ponderative" (even "optimizing") decision, of "singular adjustment", and regulating "essential" aspects of fundamental rights. The validity of the proposed canon results from its contrasted conformity with the source system and with the primary constitutional decisions. It would not be the only possible canon but it would be the one that allows optimizing the principle of local autonomy, while promoting the achievement of certain legal-constitutional principles, which compensates for the reduction that occurs in relation to others, especially those derived from "absolute" compliance with the law reservation. The functionality of an Ordinance power that requires the formal and material relaxation of the law reserve is admissible if it is considered that it does not imply an unjustified impairment of equality and, although it implies a certain sacrifice of the democratic principle (in its parliamentary aspect), in exchange, it achieves a notable reinforcement of other constitutional principles in the concerned local territorial area: of the democratic principle itself, of proportionality, of effective judicial protection and of equality itself (paradoxical as it may be). It can also involve the effective promotion of their own rights and / or other constitutional assets, most of them integrated in the clause of the social State.