The Digital Markets Act establishes central rules and enforcement for digital platforms across the European Union, but allows decentralized private enforcement on the national level. In new research, Lena Hornkohl and Barbara Justen reflect on how two recent German court cases show how national litigation can make the DMA more effective, but also highlight the need for mechanisms that aid in consistent interpretation.
When the European Union (EU) adopted the Digital Markets Act (DMA) in 2022, it sought to establish a single set of rules for its 27 Member States guiding how to regulate the largest digital platforms. Its objective is to make digital markets more contestable and fair by imposing obligations on designated “gatekeepers,” such as Google (Alphabet), Apple, Meta, and Amazon. The DMA serves as an addition to the EU’s competition law rules set out in Articles 101 and 102 of the Treaty on the Functioning of the European Union.
The European Commission is the DMA’s sole public enforcer, responsible for investigating potential infringements and imposing sanctions across the EU. Yet, the first years of DMA enforcement have revealed another, less centralized layer of enforcement: national courts. Business users, consumers, and qualified consumer organizations can invoke DMA provisions before national courts and seek remedies, such as injunctions or compensation, as private parties. A business user affected by a gatekeeper’s conduct, for example, may ask a national court to order the gatekeeper to stop an alleged infringement. In appropriate circumstances, collective action is also possible. The Commission itself describes this private enforcement as a complement to its own public enforcement.
This creates a distinctive enforcement structure: the DMA’s substantive rules are highly harmonized, and its public enforcement is centralized, while private enforcement is decentralized across national courts operating under different procedural rules and legal traditions. The DMA provides only a limited procedural framework for private litigation, meaning that national courts must draw on existing national and European law when addressing questions such as standing, jurisdiction, applicable law, and remedies.
In our recent paper, Lena Hornkohl and I examined this emerging architecture through an analysis of the first two reported judgments concerning the private enforcement of the DMA in Germany. Our analysis suggests that national litigation can make the DMA more effective and accessible. At the same time, the first cases show why mechanisms for maintaining consistent interpretation across the EU will be important.
The Meta AI case opened the door
In May 2025, the Higher Regional Court of Cologne considered a case arising from Meta’s plans to use publicly shared data from adult users of Facebook and Instagram to train its generative artificial intelligence systems. A consumer protection organization challenged the practice and argued, among other things, that it infringed on Article 5(2) DMA, which restricts the combination of personal data from different core platform services and certain third-party services without user consent.
The court ultimately rejected the substantive claim on the grounds that Article 5(2) DMA only covers targeted cross-platform profiling of individual users, not the use of partially de-identified and disaggregated data material for AI training sets. In doing so, however, it also had to interpret the scope of Article 5(2). This is significant because questions about how the DMA applies to the use of social media data for training generative AI systems had not yet been authoritatively settled by the Court of Justice of the European Union (CJEU).
The national court also addressed an important procedural issue: whether a qualified consumer organization could bring a representative action seeking to enforce DMA obligations. The decision therefore illustrates two dimensions of private enforcement. National courts may both determine who can bring a DMA claim and interpret substantive obligations whose meaning has not yet been settled at EU level.
Gmail and the reach of national courts
The second case we analyzed, decided by the Regional Court of Mainz in August 2025, illustrates the issue from a different angle.
An email service provider challenged Google’s practice of requiring users to use a Gmail account during the setup of Android devices. The claimant argued that the practice violated Article 5(8) DMA, which bans big platforms from requiring users to use one platform service, often their own, as a prerequisite for accessing another. The Mainz court granted injunctive relief.
The case raised a series of questions extending well beyond the interpretation of Article 5(8). Which companies within Google’s corporate group could be sued? Which national courts had jurisdiction? What law governed the claim? And how far could a national court’s judgment reach?
The court relied in part on concepts familiar from EU competition law. In particular, it applied the “single economic entity” concept to determine which company within Google’s corporate structure could be held responsible. It also rejected a strict “mosaic” approach to territorial jurisdiction, which would limit the court to considering the impact of Google’s behavior on just consumers in Germany. Instead, the court considered the platform-wide practice at issue as it impacted users across the EU. This shows how a national court enforcing an EU-wide obligation may have to consider conduct that extends beyond its own territory.
Why decentralized interpretation of the DMA is an issue
Generally, there is nothing unusual about national courts interpreting EU legislation. Indeed, this is a fundamental feature of the EU legal order. The distinctive feature of the DMA is the combination of highly harmonized substantive rules, centralized public enforcement, and decentralized private litigation.
However, imagine that a German court interprets an obligation in Article 5 DMA one way, while a French or Dutch court later interprets the same provision differently. Both judgments could concern the same gatekeeper and the same EU-wide business practice. A gatekeeper operating the same service throughout Europe could face different understandings of its obligations in different Member States. The gatekeeper would then have to differentiate its service, potentially leading to fragmentation of the internal market.
Different interpretations of the DMA at the national court level are particularly significant because the DMA is relatively new. Many of its concepts have not yet been authoritatively interpreted by the CJEU. Early national judgments can therefore have an outsized influence on how the regulation develops.
The Commission and the national courts
The DMA recognizes this tension. Article 39 establishes mechanisms for cooperation between the Commission and national courts. Courts may ask the Commission for information or its opinion on questions concerning the application of the DMA, and Member States must forward judgments applying the regulation to the Commission. The Commission may also submit written observations where necessary to ensure coherent application of the DMA.
These mechanisms connect private litigation with the Commission’s central enforcement role. Yet, the German cases also illustrate their limits.
Neither the Cologne nor the Mainz case resulted in a preliminary reference to the CJEU, despite the novelty of some of the questions involved (e.g. the substantive scope of Article 5(2) DMA). The Mainz proceedings also illustrate the limits of coordination where the Commission has not formally initiated proceedings.
This does not mean that national courts should always wait for the Commission or the CJEU. National courts have to apply EU law themselves, and private enforcement derives much of its value from being capable of providing timely remedies. Rather, the cases demonstrate that national courts may sometimes have to resolve novel questions of EU law in the absence of prior guidance from the EU institutions.
The result is a system in which national courts can move quickly and provide effective remedies—but may do so without waiting for the Commission or the CJEU to settle the underlying legal questions.
A new European enforcement landscape?
The first German DMA cases reveal more than two isolated disputes. They provide an early glimpse of how a supposedly centralized regulatory regime is developing a decentralized enforcement architecture.
Private enforcement has clear advantages. It can make the DMA more accessible, provide remedies where the Commission has not yet intervened, and allow disputes to be resolved without waiting for lengthy administrative proceedings. The German cases also suggest that injunctive relief may be particularly important in the early development of private DMA enforcement, where changing a gatekeeper’s conduct may be more straightforward than quantifying the resulting loss. At the same time, decentralized litigation risks undermining the DMA’s central objective of being an EU-wide rulebook for gatekeepers.
The task for the coming years is therefore not to choose between public and private enforcement. Both can play valuable and complementary roles. The challenge is to ensure that decentralized litigation strengthens the effectiveness of a common European regulatory framework without turning it into a collection of nationally interpreted rules.
Our analysis suggests that greater procedural coordination, more active use of the mechanisms connecting national courts with the Commission, and—where genuinely unresolved questions arise—greater use of preliminary references to the CJEU may be necessary to strike that balance.
Authors’ Disclosures: Lena Hornkohl is also the President of Ius Omnibus, a not-for-profit consumer protection association incorporated under the laws of Portugal, which brings inter alia collective actions, including in competition, privacy, and digital law. Neither Ius Omnibus nor Lena Hornkohl have been involved in the cases discussed in the paper and the views expressed are the ones of the authors. AI-assisted tools were employed exclusively for correction and proofreading with the aim of improving the wording and grammar of the English language. All content, analysis, and interpretation are the work of the authors. In accordance with the ASCOLA declaration of ethics, the authors have nothing else to disclose. You can read our disclosure policy here.
Articles represent the opinions of their writers, not necessarily those of the University of Chicago, the Booth School of Business, or its faculty.
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