Federal Supreme Court, 29.04.2026, 9C_169/2026
Facts
A taxpayer, who manages his own limited liability company (Sàrl), failed to declare a net salary of CHF 33,010 for the 2019 tax year. This omission was discovered during an audit of his company's tax documents. The Zurich cantonal tax authority subsequently initiated back-tax and penalty proceedings. Upon requesting information from the compensation fund (SVA), the authority discovered that the taxpayer had received other undeclared income from nine different employers between 2015 and 2020. (consid. A.a, A.b)
The proceedings were extended to the 2015, 2016, and 2020 tax years. An initial decision regarding back taxes and fines was issued. Following a hearing with the taxpayer, the proceedings were extended to the 2019 period, with a warning of reformatio in peius (a less favorable decision). Ultimately, the tax authority rejected the taxpayer's objection and set the back taxes and fines for all periods concerned (2015, 2016, 2019, 2020 for cantonal and municipal taxes; 2015, 2019, 2020 for direct federal tax). (consid. A.c, A.d)
The taxpayer appealed to the Administrative Court of the Canton of Zurich, which rejected his appeal regarding the back taxes. He then appealed to the Federal Supreme Court, requesting the annulment of the cantonal judgment, the referral of the case for further investigation, legal aid, and his own appointment as court-appointed counsel. (consid. B, C)
Legal Analysis
The Federal Supreme Court reiterates the conditions for initiating back-tax proceedings (Nachsteuer) underArt. 151 para. 1 DBG andArt. 160 para. 1 StG/ZH. Such proceedings are justified when facts or evidence, which existed at the time of the initial assessment but were unknown to the tax authority, reveal that an assessment was omitted or incomplete. These new facts (unechte Noven) must be the cause of the incomplete assessment. (consid. 5.1.1, 5.1.2)
Taxpayers are obligated to complete their tax returns fully and truthfully (Art. 124 para. 2 DBG). In case of doubt regarding the tax implications of a fact, they must not conceal it but rather declare it fully and accurately. The tax authority, for its part, may in principle rely on the accuracy of the declaration and is not required to conduct in-depth investigations or cross-checks without concrete evidence of an error or omission. An obligation to investigate only arises if the declaration contains manifest and obvious errors. (consid. 5.1.3)
Regarding the burden of proof, the tax authority bears the burden of proving facts that establish or increase tax liability, while the taxpayer must prove facts that reduce or eliminate it. This principle also applies within the framework of back-tax proceedings. (consid. 5.1.4)
The Federal Supreme Court also reiterates the qualified justification requirements for claims alleging violations of constitutional rights (Art. 106(2) of the Federal Supreme Court Act (LTF)) and for challenging the establishment of facts, which must be arbitrary ("offensichtlich unrichtig"). Mere appellate-style criticism or unsubstantiated assertions are insufficient. (consid. 2.1, 2.2, 4.2)
Application to the specific case
The Federal Supreme Court finds that the appellant failed to fulfill their obligation to declare all income for several tax periods. Income from various employers, discovered subsequently through OASI (AVS) data and confirmed by employment contracts and salary certificates, constitutes "new facts" that were unknown to the tax authority during the initial assessments. These elements fully justify the initiation of a tax back-payment procedure. (consid. 5.2, 5.3)
The Federal Supreme Court rejects the appellant's arguments challenging the lower court's establishment of facts. Their claims that the income was "fictitious" or that the facts were established arbitrarily are deemed mere unproven assertions. The appellant failed to demonstrate how the cantonal court's assessment of evidence, based on official documents, was untenable. Likewise, their constitutional grievances are dismissed as they are not sufficiently substantiated. (consid. 4.1.1, 4.1.2, 5.3)
The appellant's attempt to introduce new evidence before the Federal Supreme Court is also rejected, as they failed to demonstrate that the conditions of Art. 99(1) LTF were met. Their request for an oral hearing is deemed unnecessary, as the case is ready for judgment based on the file. (consid. 2.3, 4.1.3)
Finally, the request for legal aid is rejected, as the appeal is devoid of any chance of success. The appellant's request to be appointed as their own court-appointed attorney is described as "reckless" (mutwillig). (consid. 6.2)
Outcome
The Federal Supreme Court dismisses the appeal to the extent that it is admissible. It upholds the judgment of the Administrative Court of the Canton of Zurich and, consequently, the legality of the tax back-payments for direct federal tax (2015, 2019, 2020) and cantonal and municipal taxes (2015, 2016, 2019, 2020). The request for legal aid is rejected, and the court costs, amounting to CHF 2,000, are charged to the appellant. (Dispositif 1, 2, 3, 4)
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