Can a lawyer act for a client without proving the mandate? The Spanish Supreme Court says yes (Judgment 1056/2026)

Published on 2 September 2026 · Bufete Padilla · Civil and procedural law · Torrevieja, Elche and Moraira

There is a sentence every lawyer has read at some point, written coldly at the end of the other side's letter: "please prove the representation you claim to hold". It reaches those who send a registered letter demanding payment of a debt, those who take on an insurance company, those who propose mediation before litigating. Until now, many responded by attaching a photocopy of the client's ID, a signed engagement letter, or by having the client countersign the document "as proof of consent", just in case.

The Spanish Supreme Court has now cut that dynamic off at the root. Judgment 1056/2026 of 30 June 2026 (Civil Chamber, appeal 7385/2025) declares that a lawyer's mandate may be verbal, that no documentary form is required, and that demanding one is, in most cases, simply an excuse not to deal with the claim. And it does so in the least favourable-looking case: the right of rectification against a media outlet.

> 30-second summary. A lawyer asked a media outlet to rectify a news item, stating that he acted "under express mandate" of his client. The outlet refused because the representation had not been documented, and the lower courts upheld that refusal by applying the data protection regulation by analogy. The Supreme Court reversed: mandates are governed by the spiritualist principle, they may even be granted orally (art. 1710 of the Civil Code) and lawyers are the "typical recipients" of such mandates, so there is no reasonable ground to demand further documentation. Caveat: specific sectoral rules (banking complaints, consumer care services, art. 5 of Act 39/2015) may still require proof.

1. The facts: a rectification that was refused

A lawyer addressed a media outlet with a rectification request stating that he acted "in defence of the interests of my client and under Organic Act 2/1984 of 26 March, regulating the Right of Rectification, by express mandate of Mr Juan Ramón".

The outlet refused to publish the rectification: in its view, there was no proof that the person concerned had granted representation to the lawyer.

• The first instance court dismissed the claim by applying, by analogy, art. 23.2 of the implementing regulation of the former Data Protection Act (Royal Decree 1720/2007), which requires representation to be "clearly proven".
• The Provincial Court upheld the decision: there should have been an express designation of the representative, a copy of the principal's ID and an express reference to the granting of the power. It added that the recipient cannot be made to investigate whether any relationship exists between principal and agent.

All of that looked reasonable. All of it has now been corrected by the Supreme Court.

2. The general doctrine of the judgment

Judgment 1056/2026 lays down doctrine on representation that goes well beyond the right of rectification. These are its six essential points:

First. What representation is. It is the granting of a power of legitimation to a person to act in the interest and in the name of another, so that the representative's conduct is valid externally as if the principal had acted personally.