International Double Taxation and the Prevalence of Treaties: Cassation Order No. 16699/2025

The phenomenon of international double taxation presents a critical issue for taxpayers with foreign income. International treaties aim to prevent this burden, but what happens if domestic law appears to restrict these rights, perhaps due to a declaration error? The Order of the Court of Cassation No. 16699 of June 23, 2025, provides a decisive answer, reaffirming the prevalence of conventional international law and offering significant protection.

The Context and the Normative Conflict

In Italy, the tax credit for foreign income (Article 165 of Presidential Decree No. 917/1986, TUIR) is the instrument to avoid double taxation. However, Article 165, paragraph 8, of the TUIR seemed to condition this deduction on the correct declaration of foreign income. This limitation conflicted with international treaties, such as the Italy-Switzerland Convention of March 9, 1976, which provides for an unconditional obligation to deduct foreign taxes.

The Cassation Ruling: Constitutional Prevalence of Treaties

The Court of Cassation, in the case of S. v. A., resolved the conflict by reaffirming the prevalence of international treaty provisions more favorable to the taxpayer. This principle is based on Article 117, paragraph 1, of the Italian Constitution, which binds state legislation to international obligations.

The core of the decision is the following legal principle:

In matters of the prohibition of international double taxation, the unconditional obligation provided by international treaties, such as the Italy-Switzerland Convention of March 9, 1976, to deduct, within certain limits, from the tax payable to the Italian tax authorities the tax paid to the foreign tax authorities, also applies in cases of failure to file a tax return or failure to declare, in the filed return, income produced abroad, as the domestic law under Article 165, paragraph 8, of Presidential Decree No. 917 of 1986, interpreted in light of Articles 117, paragraph 1, of the Constitution, 75 of Presidential Decree No. 600 of 1973, and 169 of Presidential Decree No. 917 of 1986, cannot limit the prescriptive effect of those international treaties or conflict with them, as prevalence must be attributed to the latter, where more favorable to the taxpayer.

The Cassation clarifies that the right to deduct foreign taxes, guaranteed by Treaties, cannot be denied due to a mere omission or incorrect indication of foreign income. The obligation to avoid double taxation is unconditional and prevails over the formal rigidity of domestic law. Article 165, paragraph 8, of the TUIR and related provisions must be interpreted in harmony with Article 117, paragraph 1, of the Constitution, recognizing the superiority of international treaties when they offer greater protection.

Practical Implications for Taxpayers

This decision has significant implications:

• Enhanced Protection: The right to deduct foreign taxes is more robust, less tied to declarative formalities.
• Prevalence of International Law: The superiority of international tax treaties over domestic laws is reaffirmed.
• Possibility of Rectification: Even with omissions, taxpayers can obtain deductions or refunds by demonstrating the actual payment of taxes abroad and the attribution of income to the treaty provisions.

It is crucial to document the actual payment of taxes in the foreign country. The ruling protects against disproportionate consequences of a formal error, prioritizing the substance of the right not to be double taxed.

Conclusions: Equity and Tax Coherence

Cassation Order No. 16699 of 2025 consolidates jurisprudence on international taxation. It reaffirms the primary role of Treaties and ensures greater equity and protection for transnational taxpayers. It is a clear signal of Italy's commitment to a tax system consistent with its international obligations and attentive to taxpayer needs. For optimal management, the assistance of expert professionals is always advisable.