The CNMC is competent to challenge in court administrative acts and regulatory provisions ranking below the level of law when these produce obstacles in relation to effective competition in the markets. The capacity to bring legal actions is set out both in artícle 5.4 of Law 3/2013 of 4 June on creation of the CNMC and in artícle 27 of Law 20/2013 of 9 December on Ensuring Market Unity. Their application is based on the principles of need and proportionality and represents the final recourse available in situations that are especially serious in their impact on effective competition. The CNMC is one of the few competition and regulatory authorities in the world able to make use of this instrument to implement better regulation.
Some of the CNMC's legal challenges are accompanied by an expert Economic Report whose objective is to perform an economic analysis of the restrictions on competition subject to legal challenges. They sometimes incorporate a quantification of the costs that such restrictions entail for consumers and social welfare. All these expert Economic Reports are available in the page "Economic Reports" (regardless of whether they are part of legal challenges conducted within the framework of article 5.4 of the Law on creation of the CNMC or within the framework of article 27 of the Law on Ensuring Market Unity).
The legal challenges of the CNMC conducted within the framework of article 5.4 of the Law on creation of the CNMC are detailed below; while the page "Legal challenges of acts and provisions contrary to market unity: article 27 of the Law on Ensuring Market Unity" contains the legal challenges of the CNMC conducted within the framework of Market Unity.