In Belgium proceedings are underway concerning the validity of transfers of personal data to the US under the FATCA-agreement that Belgium has concluded with the US (that is identical to all other FATCA-agreements of the US with EU-member states).
These agreements are detrimental to anyone who is a tax resident of the EU and has American nationality, as the agreements export Citizenship-Based Taxation (CBT). With CBT, the US is the only country in the world that deviates from the internationally accepted system of Residence-Based Taxation (RBT).

Decision of April 2025
In April this year the Belgian Data Protection Authority [DPA] (Gegevensbeschermingsautoriteit / Autorité de protection des données) took a new decision on the matter (my article in Dutch, DPA decision in French).

Appeal
The DPA-decision was appealed by the Belgian administration.
The French organisation of the victims of the FATCA-agreements, the Association des Américains Accidentels (AAA), reported on their Facebook page and on linkedin that the hearing of the Belgian Markets Court (Marktenhof / Cour des marchés) has taken place yesterday and that the decision of the court is expected on 3 December (also mentioned on the Facebook page of the Dutch Accidental Americans group).
According to the AAA article, the following has been put forward on behalf of the Belgian victims of the FATCA-agreements:

📑 During the hearing, it was emphasized that data transfers carried out under FATCA raise serious concerns under the #GDPR, particularly regarding the principles of purpose limitation, proportionality, and data minimisation. It was also argued that the “important public interest” exception provided for in Article 49(1)(d) cannot serve as a basis for systematic and large-scale transfers to a country that does not offer equivalent safeguards, and that the Belgian tax administration has never conducted the impact assessment required by EU law.
The Court of Markets was invited to consider referring several preliminary questions to the Court of Justice of the European Union (CJEU), including:

👉 Whether large-scale transfers of personal data to the United States under FATCA comply with the fundamental principles of the GDPR;
👉Whether the “important public interest” derogation can be relied upon to justify such ongoing and generalised transfers;
👉 And whether, under Article 96 of the GDPR, Member States may continue to apply an international agreement concluded before the Regulation entered into force, when it conflicts with EU law and the Charter of Fundamental Rights.

We’ll see what happens.

Information on this site on FATCA:

• General introduction to FATCA and Citizenship-Based Taxation in Dutch
• Articles on the Belgian FATCA-procedure in Dutch and English
• Articles on FATCA in Dutch and English