The conflict in defense of local autonomy has been created by the Organic Law 7/1999 of 21 April, and through it, local authorities may, under the conditions established legitimacy, challenge laws or regulations passed by State and Autonomous Communities which adversely affects the constitutionally guaranteed local autonomy.
They are entitled to promote a conflict in defense of local autonomy the municipality or province that is the only recipient of the law or norm with force of law. In the cases of laws that are not of single recipient, complaint may be lodged by a number of municipalities involving at least one-seventh of those in the territorial scope of the law or regulation having the force of law and representing at least one-sixth of the official population of the corresponding territory and a number of provinces involving at least half of those in the territorial scope of the law or rule with force of law and represent at least half the official population. In addition, in the case of challenging legal provisions of the Canary Islands they are entitled three Islands Councils (Cabildo)and in the case of the Autonomous Community of the Balearic Islands , two island councils, even though in both cases the percentage of population required for municipalities is not reached .Laws regarding the scope of which directly affects the Basque Country may also be challenged by General Assemblies and the Provincial Councils of each Province.
To lodge the conflict in defense of local autonomy it is mandatory to reach agreement of plenary body of each local government to promote it adopted by an absolute majority of the legal number of its members. Once this agreement is reached, claimants , before lodging the conflict before the Constitutional Court, must apply, within three months from the adoption of the law or regulation having the force of law contested, for mandatory but not biding opinion to the Council of State or equivalent body of the Autonomous Community, depending on whether the territory of local authorities covers a single region or several of them. Within one month of receipt of the opinion, legitimated subjects may raise the conflict before the Constitutional Court
The Constitutional Court may rule by reasoned Decree on the inadmissibility of the complaint on base of lack of standing of individuals who have promoted it, for breach of irremediable other legal requirements or for the fact of being the controversy manifestly unfounded.
If the conflict is admissible, the Constitutional Court, in ten days, must transmit thereof to the legislative and executive of the Autonomous Community that had issued the law or regulation having the force of law and to legislative and executives bodies of the State so that they can appear in the proceedings and make submissions within twenty days. The lodging of the conflict has to be published in the relevant Official Journal.
The Judgment solving the conflict must declare whether or not a violation of the constitutionally guaranteed local autonomy existed, and to determine the allocation of the disputed competence, and resolve as appropriate on situations of fact or law created in breach of local autonomy.
In order to declare the unconstitutionality of the law or regulation having the force of law that has led to conflict in defense of local autonomy it is necessary for the Court to issue a new judgment if the Full Court decides to raise this issue once solved the conflict stating that there has been a violation of the constitutionally guaranteed local autonomy.This new process is conducted in accordance with procedural rules of the question of unconstitutionality.