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Mathieu Wiener

Mathieu Wiener is an associate at the Firm's Zürich office, in the International Tax and Global Wealth Management practice groups. Before joining the Firm, Mathieu worked in the United States Tax Court in Washington, DC. Mathieu has experience assisting individuals and families with US and international tax, wealth planning, and regulatory matters. Mathieu assists clients in interdisciplinary matters in both English and French.
During law school, Mathieu worked in the United States Bankruptcy Court for the Central District of California, and the United States Attorneys’ Office for the Central District of California, Tax Division.

On 24 May 2023, the Belgian Data Protection Authority (DPA), the authority responsible for enforcing the EU’s General Data Protection Regulation in Belgium, issued a major decision (“Decision”) concerning information exchanges pursuant to the US Foreign Account Tax Compliance Act (FATCA). The Decision declares the information reporting required of the Belgian tax authority and Belgian financial institutions under FATCA to be unlawful because it violates the privacy rights and protections afforded to Belgian residents under the GDPR, as well as the rights to a private life and protections of personal information guaranteed by the Charter of Fundamental Rights of the European Union.

Treasury and the IRS issued temporary relief procedures in Notice 2023-11 for a foreign financial institutions (FFI) that is subject to a Model 1 intergovernmental agreement (IGA) jurisdiction.
Model 1 FFIs that follow the procedures set forth in the Notice will not be in significant non-compliance with their obligations under an applicable Model 1 IGA solely because of a failure to report a required US taxpayer identification number (TIN) in relation to “preexisting accounts”.