The Belgian Court of Cassation (plenary session) validates the use of irregularly collected evidence to establish taxes

In a ruling handed down on 19 June 2025 by nine judges of the Court ("audience plénière"), the Court of Cassation confirms that evidence gathered in breach of procedural provisions may nevertheless be used for tax purposes (with certain exceptions). The Court's previous case law in this area came solely from the Dutch-speaking section of the Court. There is therefore no longer any doubt that these principles are enshrined in Belgian tax law, barring the legislative changes announced by the government.

The 'Antigone' case law

'Antigone' is the name of the case law of the Court of Cassation, according to which, in essence, the illegal use of a form of evidence does not necessarily have to be disregarded. The Court of Cassation developed this in the context of criminal law, and then transposed it to tax law (Cass. 22 May 2015, subsequently confirmed on multiple occasions). Thus, evidence tainted by illegality may serve as a basis for assessing income tax (or a VAT surcharge), unless: (1) if there is a breach of a rule prescribed on pain of nullity, (2) if the evidence has been obtained in a manner so contrary to "what is reasonably expected of an authority acting properly" that its use cannot under any circumstances be admitted or (3) if the collection of evidence carried out in an irregular manner "is contrary to a fair trial".

Confirmation by a bilingual section of the court 

Given that the previous judgments of the Court of Cassation had been handed down by the Dutch-speaking section of the First Chamber of the Court of Cassation alone, there was some doubt as to the solidity of this case law, given that it is not unusual for the two sections of the Court to have divergent case law. There is no longer any room for doubt: the judgment of 19 June 2025 from the plenary session reaffirms the rules of this case law. 

The court’s arguments and our comments 

According to the Court, the Antigone case law is not contrary to the Belgian Constitution because the principle that tax must be established by law does not concern the rules relating to the admissibility of evidence: judges would therefore have the power to make their own assessment of this admissibility. Furthermore, according to the Court, the criteria in the Antigone case law are sufficiently foreseeable, precise and foreseeable so that there is no breach of article 1 of the 1st additional protocol to the European Convention on Human Rights.

In our view, this case law is questionable given that legislative provisions do exist in the various tax codes to determine which methods of proof are acceptable to find out and establish taxable income. Therefore, in our view, judges do not have the power to set aside these legal provisions by substituting their own assessment of what is admissible or not. Furthermore, it is questionable whether the Antigone case law was foreseeable, since it arose from case law initiated by a judgment handed down on 12 May 2015, and was not preceded by any prior publicity, enabling the taxpayer to know either its entry into force or its content, unlike what happens in the case of legislative amendments, which are always preceded by the filing of preparatory documents accessible to the public. In the case submitted to the Court of Cassation, the illegality complained of by the taxpayer was committed by an investigating judge who carried out investigative acts even though they were not referred to him before 12 May 2005, and the disputed taxes were established in 2007, and therefore well before the aforementioned ruling of 12 May 2015. 

The taxpayers concerned could bring the case before the European Court of Human Rights, given the obvious retroactive nature of the case law with which they are confronted.

Hope for the taxpayers? 

Although the Court of Cassation's decision is a disappointment for the taxpayers, they can still hope that the legislature will intervene. The Belgian government has announced its intention to adopt a legislative measure. It is announcing the adoption of a clear legal framework for the use by the administration of irregular evidence, with the aim of ensuring that the tax administration respects tax procedures.