Analysis · Swiss Federal Court, 2C_506/2024, 4 May 2026 — Administrative assistance in tax matters
Legal privilege stops at the door of the law firm
In a judgment of 4 May 2026 (2C_506/2024), the Swiss Federal Court holds that correspondence exchanged between a taxpayer's lawyers and the cantonal tax authorities, once it is in the possession of those authorities, does not benefit from legal professional privilege: neither under treaty law (art. 25bis para. 3 let. c of the Switzerland-Spain tax treaty, modelled on article 26 of the OECD Model Convention), nor under Swiss domestic law (art. 8 para. 6 LAAF, art. 13 para. 1bis PA). The decision settles a question of principle and authorises the transmission to Madrid of the tax residence certificates issued by the canton of Thurgau, together with the exchanges that prepared them. Essential reading for any French taxpayer considering relocation to Switzerland, or already resident there, because the France-Switzerland tax treaty of 9 September 1966, in its article 28, rests on the same OECD clause and allows the French tax authorities to activate the same mechanism.
Analysis by Jonathan Bensaid · Tax lawyer · Paris · Geneva · Marseille · Cannes · Lisbon
— In brief
Decision
Swiss Federal Court, Second Public Law Court, 4 May 2026, 2C_506/2024
Outcome
Appeal dismissed: full transmission authorised
Question of principle
Does legal privilege cover lawyer ↔ authority correspondence held by the authority? No
Treaty framework
Art. 25bis of the CH-ES tax treaty (modelled on art. 26 of the OECD Model); ch. IV of the Protocol
Swiss domestic law
LAAF art. 7 let. a, 8 para. 6; PA art. 13 para. 1bis
French reading
France-Switzerland tax treaty, art. 28 (Amendment of 27 August 2009): same treaty architecture
— 01
Legal privilege protects the confidence, not the record the authority keeps of it
The facts are instructively ordinary. A taxpayer declares himself a Swiss tax resident, domiciled in the canton of Thurgau, and obtains from the cantonal administration, through his lawyers, several tax residence certificates for the years 2018 to 2020. The Spanish tax authorities suspect otherwise: bank cards used on Spanish territory, return flights from Barcelona, subscription of life, health, vehicle and household insurance policies in Spain, payment of property charges and telephone bills, hospital appointments, the exercise of a professional activity. On the basis of article 25bis of the Switzerland-Spain tax treaty, Madrid applies to the Swiss Federal Tax Administration and asks, among other things, to see the application form for the residence certificates, the legal provision on which they were issued, the details of the verification procedures and, where applicable, the taxpayer's tax returns.
The canton of Thurgau complies. It transmits not only the certificates but also the correspondence it exchanged with the lawyers who had requested them. The taxpayer objects: those exchanges, he argues, are protected by legal professional privilege. The Federal Administrative Court rejects his claim on 26 September 2024. The Federal Court confirms in its judgment of 4 May 2026.
The reasoning, in two stages, is remarkably clear. First stage: the requirement of foreseeable relevance (art. 25bis para. 1 of the CH-ES treaty) is amply satisfied. The purpose of the request is to establish the place of effective tax residence; the documents requested have a concrete connection with that purpose; they are apt to contribute to the verification. The standard is deliberately low: the requesting State does not have to demonstrate that the information will be decisive, only that there is a reasonable possibility that it will be (ATF 145 II 112, para. 2.1.1). The line separating a valid request from a fishing expedition is crossed only where the request has no concrete factual anchor, which is not the case where a set of objective indicia is articulated.
Second stage, and this is the main contribution of the judgment: the legal professional privilege reserved by article 25bis para. 3 let. c of the CH-ES treaty (which mirrors article 26 para. 3 let. c of the OECD Model Convention) does not cover lawyer-administration correspondence held by the administration. The OECD Commentary, no. 19.3 on art. 26, expressly limits the protection to confidential communications between the lawyer and his client. Once the document has crossed the threshold of the law firm, that is, once it has been voluntarily transmitted to a third party, here the cantonal authority, the confidence is deemed waived. Swiss domestic law points the same way: art. 8 para. 6 LAAF protects only documents in the possession of the lawyer or his auxiliary (ATF 151 II 873, para. 13.1); art. 13 para. 1bis PA protects contacts between the party and its lawyer, not letters addressed to an authority.
The Federal Court finally draws on its case law on art. 13 LLCA and criminal-law professional secrecy: where the lawyer voluntarily transmits confidential information to a third party, an insurer or an authority, "the protection conferred by that lawyer's professional secrecy in principle no longer applies" (ATF 150 IV 470, para. 5.1). The recipient third party can only invoke its own grounds for refusal, for instance official secrecy. But the official secrecy of the cantonal administration itself yields to the treaty obligation of administrative assistance.
— 02
Five operational lessons for French taxpayers
Judgment 2C_506/2024 crosses the border. The France-Switzerland tax treaty of 9 September 1966, in its article 28 as amended by the Amendment of 27 August 2009 (in force since 4 November 2010), reproduces the treaty architecture of article 26 of the OECD Model Convention. Five key points for expatriates, lump-sum taxpayers and candidates for Swiss tax residence.
1. The 1966 France-Switzerland treaty opens the same tap for the French tax authorities as for Spain
Article 28 of the France-Switzerland tax treaty, in its post-2009 wording, allows the tax administrations of both States to exchange any information that is foreseeably relevant for the application of the treaty or of domestic tax legislation. On the basis of articulated indicia, such as the use of French means of payment, household charges, insurance policies, family presence or children's schooling, the French tax authorities can therefore request from the Swiss Federal Tax Administration the same documents as those obtained by Madrid in the case commented on. Including the correspondence between the taxpayer, his lawyers and the cantonal administration that issued a residence certificate or approved an election for the lump-sum tax regime.
2. French professional secrecy under art. 66-5 does not cover lawyer-administration correspondence either
Article 66-5 of Law no. 71-1130 of 31 December 1971 protects, in general terms, opinions addressed by a lawyer to his client, correspondence exchanged between the client and his lawyer, and between the lawyer and fellow members of the bar, meeting notes and all documents in the file. The Court of Cassation has clarified that correspondence between the lawyer and a third party, for example an administration, is not protected by that provision (Cass. 1st civ., 22 Sept. 2011, no. 10-21219; Cass. crim., 9 February 2010, no. 09-81693). The Swiss Federal Court is therefore merely aligning its solution with what French law already holds: the confidence is waived once a third party receives the document.
3. Foreseeable relevance is a low threshold: the requesting State does not have to prove its case
The Federal Court confirms, and the French Conseil d'État applies the same analytical grid (CE 26 June 2017, no. 401527; CE 24 February 2023, no. 442421), that the requested State merely verifies that the documents have a connection with the facts set out in the request and that they may be useful to the foreign procedure. The actual probability of usefulness is not a criterion. The French taxpayer who believes he can block an assistance request on the ground that the French administration does not yet hold conclusive evidence is fighting the wrong battle: an articulated, even if inconclusive, set of indicia is enough to cross the threshold.
4. Actual tax residence is documented through the facts of daily life, not just certificates
The case commented on is instructive: the taxpayer held several tax residence certificates from the canton of Thurgau. That did not protect him. Why? Because the indicia put forward by the Spanish authority related to real life: payments, travel, insurance, medical care. The lesson for the French candidate for relocation to Switzerland is that an administrative certificate is only one element of the overall picture, not an irrebuttable presumption. The decisive test remains that of article 4 of the France-Switzerland tax treaty, namely permanent home, centre of vital interests and habitual abode, and it is assessed on the substance of daily life, not on administrative form.
5. The CJEU ruling in Orde van Vlaamse Balies does not neutralise administrative assistance
The CJEU judgment, Grand Chamber, 8 December 2022, Orde van Vlaamse Balies (C-694/20) invalidated, under DAC6, the obligation imposed on intermediary lawyers to notify third parties of their inability to report on grounds of professional secrecy. The Court stressed the importance of lawyer-client confidentiality as a corollary of the rights of the defence (art. 7 and 47 of the Charter). But that protection, like the one established by the ECtHR in Michaud v. France, 6 December 2012, no. 12323/11, concerns the internal relationship between lawyer and client. It does not preclude the transmission, within the framework of administrative assistance, of documents that have left the sphere of that relationship for the filing cabinets of a third-party administration. The hierarchy is constant: strong protection of the confidence; permitted transmission of its record.
— 03
Our approach at the firm
The firm advises individuals, executives and families on the structuring of their international tax residence: preparing the relocation, electing the Swiss lump-sum tax regime (notably in the cantons of Vaud, Valais, Ticino, Zug and Bern), negotiating expenditure-based taxation with the cantonal administration, and articulating the arrangement with fiducie structures and wealth-holding vehicles. Judgment 2C_506/2024 reinforces a discipline the firm regards as cardinal: whatever is written to an administration may be transmitted to any partner administration under an exchange-of-information agreement. Notes, memoranda and submissions filed with a cantonal authority during the examination of an election, a residence certificate or a ruling are, by definition, liable to land one day on the desk of a French tax inspector.
The resulting discipline is threefold. First, submissions addressed to the cantonal authority are drafted as defence pleadings: every word matters, every argument set aside must be documented, and no gratuitous factual assumption appears in them. Second, the firm's internal analyses, opportunity notes and trade-off assessments, in short everything that constitutes the advice, remain strictly within the lawyer-client sphere, where the protection remains intact, under Swiss law as under French law. Third, the firm documents in parallel the factual substance of residence: a presence log, invoices from local service providers, Swiss bank statements, insurance contracts anchored in Switzerland, and an effective professional activity on Swiss soil, which together form, in the event of a challenge, the first line of defence before the French tax authorities.
For taxpayers already domiciled in Switzerland who face a request for administrative assistance issued by France, the firm acts on two fronts: in Bern, before the Swiss Federal Tax Administration and, on appeal, the Federal Administrative Court and then the Federal Court; and in Paris, before the audit services of the French tax authorities and, where necessary, the tax courts. Coordinating those two procedures, their timetables, suspensive effect and the scope of the disputed documents, is the very object of the firm's intervention.
— Frequently asked questions
What judgment 2C_506/2024 changes for French taxpayers
I am a Swiss tax resident under the lump-sum regime. Can the French tax authorities obtain my cantonal file?
Yes, through the channel of article 28 of the France-Switzerland tax treaty of 9 September 1966 (as amended by the Amendment of 27 August 2009). Provided they articulate a substantiated suspicion, since foreseeable relevance does not tolerate a fishing expedition but does accept a set of indicia, the French tax authorities can send the Swiss Federal Tax Administration a request covering the file held by the cantonal authority that granted the lump-sum regime: application form, supporting documents, preparatory correspondence, the annual expenditure retained, the ruling. Judgment 2C_506/2024 confirms that such correspondence, even where it passed through your lawyer, can be transmitted once it is in the hands of the administration.
Can my Swiss lawyer refuse to produce his own working files?
Yes: art. 8 para. 6 LAAF protects what remains with the lawyer or his auxiliary. The Federal Court confirmed this in ATF 151 II 873 (judgment 2C_116/2023 of 2 May 2025), concerning a request targeting a lawyer personally suspected of holding undeclared accounts: as long as the documents remain within the perimeter of the law firm, legal professional privilege bars their transmission. The distinction is fundamental: the confidence remains protected as long as it does not leave the firm. It is its voluntary transmission to a third party, whether administration, bank or insurer, that lifts the protection (ATF 150 IV 470).
The CJEU strengthened lawyers' professional secrecy in Orde van Vlaamse Balies. Does that not stand in the way of administrative assistance?
No. The CJEU judgment of 8 December 2022 (C-694/20) invalidated, within the framework of the DAC6 directive, the obligation imposed on an intermediary lawyer to notify other intermediaries of his inability to report. The Court based its decision on articles 7 and 47 of the Charter of Fundamental Rights, namely the right to respect for communications and the rights of the defence. But the scope of that decision is limited to the internal relationship between the lawyer and his client. It does not neutralise the treaty mechanisms for exchanging information in tax matters, which cover documents already held by the requested administration. The same logic follows from the ECtHR judgment in Michaud v. France, 6 December 2012, no. 12323/11: confidentiality protects the advice, not the administrative record.
Can my exchanges with the French tax authorities, transmitted by my lawyer, be passed on to Switzerland through administrative assistance?
Yes, by symmetry. The logic of judgment 2C_506/2024 is universal: a document that has left the sphere of the law firm to join the filing cabinets of an administration is, by definition, no longer a lawyer-client confidence. Switzerland, like any State that is a partner of France in administrative assistance matters (whether through a bilateral treaty, the OECD-Council of Europe Multilateral Convention of 25 January 1988, or Directive 2011/16/EU for Member States), can obtain copies of correspondence that your French lawyer may have addressed to the French tax authorities, provided the request satisfies the foreseeable-relevance test. French professional secrecy under art. 66-5 of the 1971 law does not stand in the way, in line with the case law of Cass. 1st civ., 22 Sept. 2011, no. 10-21219.
What indicia can the French tax authorities articulate to justify an assistance request?
The set of indicia relied on by the Spanish authority in case 2C_506/2024 is emblematic and prefigures what the French tax authorities could put forward against a taxpayer declaring himself Swiss: use of bank cards on French territory, flight bookings departing from a French airport, subscription of life, health, vehicle and household insurance policies in France, payment of French property charges and telephone bills from French accounts, medical appointments in France, exercise of a professional activity on French territory. None of these indicia is, on its own, decisive. It is their accumulation that reaches the threshold of foreseeable relevance. The defence must therefore be built on substance, that is, objective evidence of Swiss daily life, and not on the mere production of administrative certificates.
What remains of legal privilege in an international administrative assistance procedure?
There remains, and it remains strong, a zone of certain protection: all documents that stay within the material perimeter of the law firm (internal notes, memoranda, unsent drafts, strategic analyses, lawyer-client correspondence). That zone is guaranteed by art. 8 para. 6 LAAF in Switzerland, by art. 66-5 of the 1971 law in France, and by articles 7 and 47 of the Charter at EU level. Outside that zone, as soon as the document is voluntarily handed over to a third party, whether an administration, a bank, a counterparty or an opposing party, the protection gives way to the rules applicable to the recipient (official secrecy, banking secrecy, and so on), rules which, in tax matters, do not withstand the treaty obligation of assistance.
Does the judgment affect taxpayers who reside in France but hold an account or a file in Switzerland?
Indirectly, yes. The logic of judgment 2C_506/2024 is primarily aimed at candidates for Swiss residence, but it applies a fortiori in the other direction: any document held by a French administration, such as tax returns, exchanges with an audit service or advance rulings, can in principle be transmitted to partner administrations on the basis of assistance agreements. For French residents holding assets in Switzerland, the main risk is no longer the communication of Swiss cantonal files (see the AEOI, the automatic exchange of information in force since 2018), but rather the cross-transmission by France of their own submissions to Switzerland, Luxembourg or any other partner State: a point to factor in upstream of any cross-border transaction.
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— See also
Related pages
Topics frequently connected with international administrative assistance, legal privilege and tax residence.
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