Shareholders’ agreements before the Spanish Supreme Court: the most recent doctrine (2025-2026)

The enforceability of a shareholders’ agreement does not depend solely on what the parties agree, but on the force the legal system affords it once a dispute arises. That force is ultimately delimited by the First Chamber of the Spanish Supreme Court, whose doctrine on shareholders’ agreements is worth knowing before drafting. Over recent months, two judgments — STS 1713/2025 and STS 674/2026 — have clarified how far such an agreement reaches and where its limits lie. We analyse them below. For the wider commercial context in which we advise on these instruments, see our commercial law practice.

The agreement does not bind the company

A shareholders’ agreement is the arrangement that shareholders enter into outside the articles of association. As between the signatories it has full contractual force under article 1257 of the Spanish Civil Code, but article 29 of the Spanish Companies Act (Ley de Sociedades de Capital, LSC) is categorical: "agreements kept private between the shareholders shall not be enforceable against the company".

The consequence, long settled, is emphatic: a corporate resolution cannot be annulled merely because it breaches a shareholders’ agreement (Supreme Court judgment of 6 March 2009, RJ 2009/2793), and that holds even where every shareholder signed the agreement. A party faced with a breach does not challenge the resolution under article 204 LSC; instead, it seeks performance of the agreement against the signatories. That is the rule. The two recent judgments are the two qualifications that have redrawn it.

The unanimous agreement and good faith (STS 674/2026)

Citation. STS 674/2026 of 5 May (ECLI:ES:TS:2026:1980), First Chamber.

Facts. Two branches of a family which, through inheritance, had come to hold the entire share capital governed their relations by way of a unanimous shareholders’ agreement. A resolution was passed distributing dividends in kind without any provision to that effect in the articles, and one of the signatories challenged it.

Legal question. May a shareholder who signed a unanimous agreement challenge a resolution adopted in performance of it?

Ratio decidendi. The Supreme Court says no: to do so is contrary to good faith under article 7 of the Civil Code and to the doctrine of estoppel by one’s own acts, because the other signatories were entitled to rely on the shareholder conducting itself in accordance with what had been agreed. It adds that the unanimity required for certain decisions may be regarded as satisfied through the agreement itself, without the need for a formal resolution in general meeting.

Doctrine. It confirms and extends the line taken in STS 103/2016 of 25 February (RJ 2016/635), reiterated by the Supreme Court judgment of 7 April 2022. The unanimous agreement remains unenforceable against the company, but the signatory is bound by its own conduct: its effect is indirect, yet real.

The validity of the agreement and its limits (STS 1713/2025)

Citation. STS 1713/2025 of 26 November (ROJ 5316/2025), First Chamber.

Facts. An agreement imposed de facto unanimity for the adoption of certain resolutions and had no fixed term, although one was ascertainable.

Doctrine. The Supreme Court upholds its validity under the freedom of contract in article 1255 of the Civil Code and accepts that de facto unanimity may be a legitimate mechanism for protecting minorities. But it introduces a significant limit: it subjects shareholders’ agreements to the mandatory rules of company law, so that they may neither contradict those rules nor hollow out the statutory structure of the company. Freedom of contract legitimises almost anything as between shareholders, but it does not permit mandatory law to be circumvented.

Our assessment

Read together, the two judgments strike a clear balance. The Supreme Court firmly protects an agreement entered into by all the shareholders — to the point of preventing a signatory from going back on it — while at the same time refusing to allow that agreement to be used to evade mandatory law or to distort the company. The unanimous agreement is therefore effective, but not unlimited.

From that reading we draw three drafting decisions we would recommend: that the agreement be unanimous — signed by all, with accession clauses for anyone joining later — so that good faith protects it; that it have an ascertainable duration; and that it be coordinated with the articles of association, taking into them whatever must be enforceable against the company and respecting mandatory rules. At RCM Legal we draft and review shareholders’ agreements with this doctrine in hand, anticipating the dispute and checking that each clause withstands the tests of enforceability and validity the Supreme Court applies. If you are negotiating an agreement, bringing in an investor or reviewing one already signed, tell us about your case: we will tell you what force each provision really has and how to strengthen it.