A New Era in the Joinder of Cases Considering the Constitutional Court’s Recent Decision
Introduction
The Turkish Constitutional Court (“TCC”), in its decision dated 17 June 2025 and numbered E.2024/237, K.2025/137 (“Decision”), decided that significantly reshapes civil procedural law. The Court annulled the phrase “…and this decision shall be binding on the other court” contained in Article 166(1) of the Code of Civil Procedure No. 6100 (“CCP”), which rendered a joinder decision by one court within the same judicial district absolutely binding on another court. This ruling not only modifies a technical procedural rule but also conveys a strong message regarding the hierarchy and supremacy of constitutional principles within the Turkish legal order.
At the heart of the Decision lies a tension between two fundamental principles that underpin modern constitutional democracies: on the one hand, the constitutional guarantee of the lawful (natural) judge enshrined in Article 37 of the Constitution, and on the other, the principle of judicial economy regulated under Articles 141 of the Constitution and 30 of the CCP. While judicial economy aims to ensure that proceedings are concluded within a reasonable time and without unnecessary costs, the lawful judge guarantees the right of every individual to have their case heard before an independent and impartial court predetermined by law. In this Decision, the TCC clearly emphasized that the pursuit of procedural efficiency and speed cannot override a fundamental safeguard that constitutes the essence of the right to a fair trial. This reasoning reaffirms the primacy of constitutional rights over procedural expediency and underlines that procedural codes, however practical or efficiency-oriented, must always operate within the constitutional boundaries of fundamental rights and freedoms.
This article first outlines the legal framework of the joinder of cases and the annulled rule. It then examines the TCC’s reasoning in detail through the lens of the lawful judge guarantee. Subsequently, it discusses the potential procedural implications of the Decision- particularly the emergence of “joinder disputes” between courts- and finally evaluates the significance of the ruling for Turkish procedural doctrine and judicial practice.
The Institution of Joinder of Cases and the Annulled Provision
The joinder of cases regulated under Article 166 of the CCP is one of the clearest manifestations of the principle of judicial economy. Its primary purpose is to allow related cases -those arising from the same or similar causes, or where the judgment in one would affect the other- to be heard together under a single file. This ensures a faster and less costly process, facilitates joint assessment of evidence, and most importantly, prevents contradictory judgments between courts. Under the rule, cases pending before courts of the same level and jurisdiction within the same judicial district could be joined either upon request or ex officio by the court before which the second case was filed.
The annulled phrase “…and this decision shall be binding on the other court” played a crucial role in the operation of this mechanism. It made the joinder decision rendered by the court handling the second case binding and non-contestable for the first court. Consequently, the first court could not review whether the conditions for joinder were met (e.g., whether the cases were truly connected) nor could its object to the decision. In practice, it was compelled to accept and transfer the file. Moreover, pursuant to Article 168 of the CCP, such joinder decisions could only be appealed together with the final judgment, making immediate judicial review of their legality impossible.
This created an unusual and asymmetric power dynamic between courts of the same level. Normally, when a dispute arises between courts of equal standing regarding jurisdiction or competence, it is resolved by a higher judicial body, such as the Regional Court of Appeal or the Court of Cassation, under Articles 21–23 of the CCP through the determination of judicial venue. A court of equal rank cannot issue a binding procedural order upon another court. The annulled phrase, however, created an exception by granting the later-seized court the power to issue a decision binding on the earlier-seized court. TCC’s annulment eliminates this procedural anomaly and reinstates the traditional, symmetrical relationship between courts of equal standing. Accordingly, the Decision safeguards not only the rights of the parties but also the procedural integrity and hierarchical logic of the judiciary.
The Constitutional Court’s Assessment: A Perspective Through the Lawful Judge Guarantee
The Principle of the Lawful (Natural) Judge as a Constitutional Safeguard
Article 37 of the Constitution, titled “Guarantee of the Lawful Judge”, provides that “No one shall be tried by any court other than the one that they are legally subject to.” In the TCC’s jurisprudence, this provision is interpreted as synonymous with the broader principle of the natural judge and is considered a fundamental component of the right to a fair trial. The principle is grounded by two elements: legality and predetermination. Legality requires that the establishment, jurisdiction, and competence of courts be determined by law, while pre-determination demands that such rules be set before any dispute arises. Its aim is to prevent legislative or executive interference with the judiciary by establishing ad hoc courts or manipulating the jurisdiction of existing ones to influence outcomes, thereby protecting individuals against arbitrariness. This safeguard also constitutes the foundation of the right to be heard by an independent and impartial tribunal established by law under Article 6 of the European Convention on Human Rights (“ECHR”).
Grounds for Annulment: Absence of an Effective Corrective Mechanism Against Arbitrariness
In its majority opinion, the TCC acknowledged that the joinder of cases is not inherently unconstitutional and serves legitimate objectives such as procedural efficiency. However, it concluded that the contested provision lacked sufficient and effective safeguards against arbitrary interference with the lawful judge guarantee.
The underlying logic of the Decision can be summarized as follows: procedural rules that permit a case to be transferred from one court to another can only be constitutionally valid if they include mechanisms to prevent arbitrariness. The annulled rule, however, allowed the second court to render a joinder decision, even where no genuine connection existed between the cases, and made this decision binding upon the first court without any effective corrective mechanism. According to TCC, the core problem was the absence of any procedural remedy capable of reversing an unlawful joinder decision and restoring the case to its rightful court. The Court also emphasized that the severance of cases under Article 167 of the CCP did not remedy this deficiency: even if the first court believed the joinder was erroneous, it would still be obliged by law to continue hearing both cases, thereby perpetuating the violation of the lawful judge guarantee.
Possible Disputes Between Courts After the Removal of Binding Effect
While the TCC’s ruling reinforces the lawful judge guarantee, it also introduces a procedural gap and a new potential source of disputes. The most significant change resulting from the annulment of Article 166(1) is the transformation of the joinder decision’s nature: previously, it was binding; now it is more akin to a proposal or request for concurrence. Accordingly, the court hearing the first case may now review and either accept or reject the joinder decision sent by the second court. If the first court refuses, an unregulated procedural conflict, which might be termed a joinder dispute, may arise. Although it is conceivable that the higher court (Regional Court of Appeal) could resolve such disputes by analogy to Articles 21–23 CCP governing jurisdictional conflicts, there is currently no explicit legal regulation on this issue.
Practically, this means that the first court can now refuse to accept the transfer if it finds that the conditions for joinder (particularly the connection under Article 166/4 CCP) are not met. Such a situation could create a “negative jurisdictional conflict” where both courts decline to hear the case. Ironically, while the Decision strengthens a fundamental constitutional safeguard, it may in the short term hinder judicial efficiency, the very principle the annulled rule was designed to promote.
Conclusion
By removing the binding nature of the joinder decision under Article 166(1) CCP, the Constitutional Court has recalibrated the delicate balance between the right to a fair trial and the principle of judicial economy in Turkish procedural law. The Decision reaffirms that the guarantee of the lawful judge—an inseparable component of the right to a fair trial—takes precedence over efficiency and speed, thereby reinforcing the supremacy of constitutional rights. It also illustrates that procedural provisions must always be interpreted through a rights-protective lens rather than a rigidly formalistic one.
Nevertheless, the ruling leaves a legal vacuum that may lead to uncertainty and new procedural disputes in practice. While applying the CCP’s rules on jurisdictional conflicts by analogy could serve as a temporary solution, the most appropriate and lasting remedy would be legislative intervention. The legislature should amend Article 166 and its subsequent provisions to clearly define the procedure to be followed in cases of disagreement between courts regarding joinder.
Ultimately, the TCC’s Decision not only reshapes the institution of joinder but also reminds all legal practitioners of their duty to scrutinize procedural mechanisms through the filter of constitutional guarantees. It stands as an important milestone that will contribute to a more rights-oriented interpretation of procedural law and to the deepening of the rule of law in the Turkish legal system.
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