Tribunal Constitucional Overturns the Supremo on IUC and Restores the Rebuttable Presumption — Former Vehicle Owners Recover the Right to Prove the Sale and Shake the Fisco Bill

The Tribunal Constitucional (TC, Constitutional Court) has come down on the side of the contribuinte (taxpayer) in the long-running dispute over who is liable for the Imposto Único de Circulação (IUC, Unique Circulation Tax) when a vehicle has been sold but the buyer never recorded the title transfer at the Conservatória do Registo Automóvel. In a string of acórdãos through 2025 and 2026, capped by a fresh ruling reported this week by Jornal de Negócios, the TC has held that Article 3, no. 1 of the Código do IUC (CIUC) — the provision that pins the annual road tax on whoever appears as proprietor in the registry, without allowing rebuttal — is unconstitutional.

The practical effect is to wipe out the Supremo Tribunal Administrativo (STA, Supreme Administrative Court) interpretation that the Autoridade Tributária e Aduaneira (AT, Tax and Customs Authority) had been leaning on since the STA's uniformising acórdão of 2024. That ruling had read the CIUC as creating a presunção inilidível (irrebuttable presumption) — the registered owner pays, full stop, regardless of whether the car had passed to a new owner who simply failed to file the change. The TC's read is the opposite. Tax law, under the constitutional equality (Articles 13 and 103) and equivalência (equivalence) principles, cannot levy a tribute on a person who has already parted with the asset that justifies the tax. The Imposto Único de Circulação is structured as a benefit-tax tied to road use and externalities — a former owner who no longer drives the vehicle should not bear the bill.

The TC therefore reinstates a presunção ilidível (rebuttable presumption): the person listed in the registry is presumed to be the proprietor for IUC purposes, but the contribuinte can rebut that presumption by producing evidence of the prior transfer. Acceptable proof on the books today includes the declaração de venda signed by both parties, the contrato verbal de compra e venda backed by payment evidence, the vehicle's transfer notice to the Instituto da Mobilidade e dos Transportes (IMT), insurance termination notices, or sworn declarations from the buyer. Lower-court jurisprudence from the Tribunais Administrativos e Fiscais (TAF) had already begun to drift in this direction; the TC ruling now hardwires the constitutional ceiling and forces the STA to align.

The downstream impact for drivers — and for the AT — is material. Portugal's vehicle fleet runs at roughly 7.2 million light vehicles per ACAP. Transfers that go unregistered are a chronic friction point: sellers in good faith deliver the keys and the title document, the buyer fails to file with the Conservatória within the 60-day legal window under DL 54/75, and the seller continues to receive the annual IUC nota de cobrança. Under the STA reading, the AT could enforce the bill against the seller and let the seller pursue the buyer in civil court for reimbursement — a procedure that almost never recovered the bill. Under the TC reading, the AT will have to chase the actual user of the vehicle.

For the AT, the operational consequence is a workflow rebuild. Notas de cobrança will now have to be paired with a verification path that accepts rebuttal evidence at the impugnação stage, rather than the current near-automatic rejection. Tax-litigation specialists expect a wave of impugnações judiciais and pedidos de revisão against bills issued from 2021 onwards, where the statute of limitations is still open. The AT has not yet published a guidance note on how it will process the back-file under the new constitutional frame.