Multiple Litigation System in the Social Jurisdiction (Joinder of Actions, Test Case Procedure, and Extension of Effects)

Abstract

This paper offers a systematic and up-to-date analysis of the Multiple Litigation System (SLM) following the far-reaching reform introduced by Royal Decree-Law 6/2023 and Organic Law 1/2025. It explains how joinder of actions and proceedings, test-case litigation, and the extension of effects together form a graduated model designed to manage large-scale repetitive litigation in the social jurisdiction, preventing contradictory decisions and strengthening procedural economy. The author clarifies the constitutional foundations of the SLM, particularly its connection with the principle of equality in the application of the law (Art. 14 of the Spanish Constitution) and the case law of the Constitutional Court. The study precisely defines the scope of application of the system, distinguishing the proceedings in which it is appropriate from those in which it is excluded for structural or legal reasons. It also analyses the interaction between the SLM and the judicial reorganisation resulting from the creation of the Courts of Instance, highlighting its practical impact on the management of repetitive claims. The paper provides a detailed examination of the functioning of the test-case procedure and the extension of effects, offering interpretative criteria to fill existing normative gaps. It further establishes the structural difference between the SLM and collective disputes, clarifying when each mechanism should operate. Finally, it assesses the advantages and drawbacks of the system and proposes measures aimed at ensuring its correct application without undermining the right to effective judicial protection.