In European Union law, sincere cooperation (Article 4(3) TEU) is one of the foundational principles of the European Union, which determines that the Union and the Member States are required to implement any necessary measures to guarantee compliance with the duties stemming from the Treaties "in full mutual respect".[1]
Sincere cooperation is mentioned explicitly not only in the Treaty on European Union but also in the Court of Justice of the EU's case law, applicable to different exclusive, shared, supporting competences, such as the environment, the Area of Freedom, Security, and Justice, public health, competition rules governing the internal market, and others.[2] [3] [4]
The jurisprudence of the CJEU has elaborated on four main responsibilities that derive from the principle of sincere cooperation:
1) An obligation for respect and assistance between the EU and Member States in attaining the Treaties' objectives
2) Member States have an active obligation to cooperate and comply with original and derivative European law
3) Member States need to refrain from taking any measures that would impede the aims and goals of the Union
4) Member States should facilitate the institutions of the EU to accomplish the Union's objectives.
In Article 10 of the Treaty establishing the European Community (TEC) from 2002, the provision contains the outlines of what is today known as "the principle of sincere cooperation":However, since the Treaty of Lisbon the provisions have been enhanced through Articles 4(3) and Article 24(3) of TEU:[5] Initially, it is notable that sincere cooperation gained a more significant prominence in the founding treaties and a more central position, that follows immediately after the Union's values. More importantly, the relationship with the principle of sincere cooperation has been widened as a two-way street, that does not only involve the Member States but also requires reciprocity from the Union's institutions.[6] This balance can be witnessed in Article 13 TEU:This balance with sincere cooperation between inter-parties relationship, regarding the Member States and the Union, has been extended to intra-institutional relationships, within the EU. The constitutional origin of this intra-institutional commitment to sincere cooperation could be traced in CJEU case law, such as the case Greece v Council from 1986[7] and Luxembourg v Parliament from 1981,[8] where the Court established that "the operation of the budgetary procedure..., is based essentially on inter-institutional dialogue. That dialogue is subject to the same mutual duties of sincere cooperation which, as the Court has held, govern relations between the Member States and the Community institutions...".
Aside from the extension of sincere cooperation on an intra-institutional level, it is crucial to underscore that there is a mixed relationship between sincere cooperation (Article 4(3) TEU), and the requirement of unity and close cooperation. The latter are duties applicable to the Union's Common Foreign and Security Policy.[9] For instance, Article 24 TEU, underlines:
This specific CFSP obligation is to a certain extent related to the principle of sincere cooperation but has its own space in the Treaty as these two principles could be perceived as distinct: the principle of close cooperation under CFSP is applicable "once a decision for mixed external action has been made", as opposed to the principle of sincere cooperation that in other competences applies before, while the decision has been made, and after it comes into force. As a result, and due to the sensitivity of EU external action regarding close cooperation between the Members, the scope of Article 24 leaves little room for exemptions through its direct language ("shall work", "shall refrain", "actively and unreservedly"). The need for a close cooperation among members in this special competence is even more accentuated since the Court of Justice, with the exception of Article 40 TEU and Article 275 TFEU, does not have jurisdiction over CFSP.
A legal limit to sincere cooperation has been imposed within the same Article 4:Right before the principle of sincere cooperation is introduced, the legislator notes the importance of national identities. Therefore, by looking at Article 4(2) and 4(3) TEU simultaneously, there are "constitutional limits in an institutional and procedural framework" that are inherent to the framework around which the principle of sincere cooperation operates.[10] Simultaneously, this does not infer that national identity enjoys supreme power within the Union's system, yet it is balanced against the "uniform application of EU law" through a composite constitutional structure of the CJEU and the national courts and institutions. Precisely for this to function in practice, the principle of sincere cooperation is invoked again as it its importance is crucial for the coordination of this multi-dimensional jurisprudence.
Consequently, this once again, emphasizes the interconnection between national identities, sincere cooperation, and the Union's foreign policy. To this end, the Member States concerned for their rights to sovereignty within this multi-dimensional jurisprudence that requires sincere cooperation on an international level, have emphasized the non-exclusionary rights through Declarations 13 and 14 of the Lisbon Treaty: the mutual political solidarity and sincere cooperation on the CFSP EU level, "do not affect the responsibilities of the Member States... for the formulation and conduct of their [national] foreign policy...".
The EU legal order and the ECHR legal system are two separate ones, and while the EU is not a member of the Council of Europe, the Member States of the Union are; consequently, the principle of sincere cooperation has appeared in cases before the European Court of Human Rights.
The case Könyv-Tár Kft and Others v. Hungary (Application No. 21623/13) concerned three applicant companies, all schoolbook distributors, which claimed that the creation of a state monopoly on school books is a breach of Article 1 of the Protocol No.1, namely the peaceful enjoyment of possessions. In the ECtHR deliberations, the Court has made the following arguments regarding the principle of sincere cooperation as part of the European Union legislation:[11] Here, the ECtHR notes the importance of sincere cooperation on a judicial level between the Court of Justice of the European Union and the national courts, while also stipulating that the Union's authorities have a responsibility to observe the practice of sincere cooperation within their conferred competence.
While the respect for national identities has been enshrined in Article 4 TEU, it is notable that post-Lisbon, for any competences that are not conferred on the Union where the Member States could exercise their sovereignty, they are still restricted in that they need to facilitate the Union's objectives and goals within their sovereignty—according to the principle of sincere cooperation.[12] Consequently, Member States' interactions with the Union is continuously guided by the aforementioned principle. This has been reflected in CJEU case law in different areas of competence across the EU.
In Case C-516/22 Commission v United Kingdom of Great Britain and Northern Ireland decided on 14 March 2024, the Court assessed the judgment of the Supreme Court of the United Kingdom in the case Micula v Romania.[13] The Supreme Court of the United Kingdom in the aforementioned case ordered Romania to pay a compensation to Swedish investors, despite the Commission prohibiting Romania to do so, as it was incompatible with EU law.[14] As a result of the decision of the Supreme Court of the United Kingdom, the CJEU declared that "the United Kingdom has failed to fulfil its obligations under EU law":
Therefore, the Court establishes a direct link through the principle of sincere cooperation between the national courts, and the institutions of the European Union:
In the case (C-454/22), Commission v Latvia, the European Commission brought the Republic of Latvia before the Court for failing to adopt all the legal provisions by transposing "necessary to comply with Article 124(1) of Directive (EU) 2018/1972 of the European Parliament and of the Council of 11 December 2018 establishing the European Electronic Communications Code".[15] Consequently, the Court has elaborated on the role of Member States in the process of transposition of a Directive, according to the principle of sincere cooperation:
In the case (C‑316/19), Commission (supported by the European Central Bank) v Slovenia, the Commission brought the Republic of Slovenia before the Court because it alleged that it breached the Union's law and failed to cooperate sincerely "by unilaterally seizing at the premises of the Banka Slovenije (Central Bank of Slovenia) documents connected to the performance of the tasks of the European System of Central Banks (ESCB) and of the Eurosystem".[16] The Court, in its findings, focuses on the reciprocity of the relationship between the Union's institutions and the Member States:Therefore, the Court establishes that even in a situation where there is a breach of Union's law on the side of the Member State, thus failing to adhere to the principle of sincere cooperation—reciprocity remains a core component of this principle, and a way to continue to uphold it is by providing assistance from the Union's institutions.