Meta and TikTok have dealt a blow to the European Commission’s social media rule book, pressing the EU executive to codify how it calculates the number of users on online platforms.

The General Court at the Court of Justice of the European Union sided with the social media companies on Wednesday in their challenge of an annual supervisory fee the European Union charges to pay for the enforcement of its tech rulebook, the Digital Services Act (DSA).

It’s the first major court loss for the Commission over the DSA, which entered into force in 2022 and can be wielded to fine social media and e-commerce platforms up to 6 percent of their global annual revenue. The EU has yet to finalize investigations under the law.

At the heart of the case are platforms’ disagreements with how the EU calculated the fee. The Commission directly supervises “very large online platforms” with over 45 million average monthly users in the bloc.

Meta and TikTok challenged the European Commission’s decisions imposing so-called supervisory fees in 2024. These fees are meant to support the Commission’s work overseeing the very platforms that pay it — an extension of the “polluter pays” principle often used in environmental policy — and are proportionate to the number of users platforms have in the EU.

The EU’s General Court said in its ruling the Commission should have passed a separate set of rules about how users are calculated before determining the fees. Judges gave the Commission a year to draft a text on how it calculates platform users, or else potentially refund the platforms’ 2023 fees.

The EU executive has already been working on such rules, called a delegated act.

The Commission said the court merely ruled against it on procedure and not substance. “The Court confirms our methodology is sound: no error in calculation, no suspension of any payments, no problem with the principle of the fee nor the amount,” said spokesperson Thomas Regnier.

Meta said in a statement that the judgement “will force the European Commission to reassess the unfair methodology being used to calculate these DSA fees,” adding it “looks forward to the flaws in the methodology being addressed.”

TikTok “welcomed” the decision and will “closely follow the development” of the case, company spokesperson Paolo Ganino said.