Crotty v An Taoiseach was a landmark 1987 decision of the Irish Supreme Court which found that Ireland could not ratify the Single European Act unless the Irish Constitution was first changed to permit its ratification. The case, taken by Raymond Crotty formally against the Taoiseach (then Garret FitzGerald), directly led to the Tenth Amendment of the Constitution of Ireland (which authorised the ratification of the Single Act) and established that significant changes to European Union treaties required an amendment to the Irish constitution before they could be ratified by Ireland. As a consequence, Ireland, uniquely in the EU, requires a plebiscite for every new, or substantive change to a, European Union Treaty. The substantive issues in the case revolved around the interpretation of Part III of the Single European Act which codified cooperation on foreign policy matters between the governments of the then twelve member states of the European Economic Community – referred to as European Political Cooperation – into an international agreement. The majority of the Court ruled that if the state ratified Part III, it would amount to an unconstitutional delegation of the state's external sovereignty. The dissenting judges argued that the provisions only constituted a requirement to listen and consult.

Supreme Court decision

The Supreme Court decision was split into two parts. The first dealt with the constitutionality of the European Communities (Amendment) Act 1986 and consequently the first two parts of the Single European Act. The Constitution requires that the Supreme Court only hand down a single judgement in such circumstances. The second part of the Court's decision considered Raymond Crotty's challenge to the proposed ratification of Part III of the Single European Act. As this did not involve a challenge to the constitutionality of legislation, each judge is free to hand down separate judgements. In a 3-2 decision a majority of the Court found Part III to be repugnant to the Constitution.

European Communities (Amendment) Act 1986

The judgement of the Court on the constitutionality of the 1986 Act was given of Finlay CJ. The Court first considered where the 1986 Act could take advantage of the Third Amendment which granted constitutional immunity to legal measures which were necessitated by membership of the European Communities. "It is clear and was not otherwise contended by the defendants that the ratification by the State of the SEA (which has not yet taken place) would not constitute an act 'necessitated by the obligations of membership of the Communities'. It accordingly follows that the second sentence in Article 29, s. 4, sub-s. 3 of the Constitution is not relevant to the issue as to whether the Act of 1986 is invalid having regard to the provisions of the Constitution. (para. 6)" The Court then continued: "It was contended on behalf of the plaintiff that any amendment of the Treaties establishing the Communities made after 1 January 1973, when Ireland joined those Communities would require a further amendment of the Constitution. It was contended on behalf of the defendants that the authorisation contained in the first sentence of Article 29, s. 4, sub-s. 3 was to join Communities which were established by Treaties as dynamic and developing entities and that it should be interpreted as authorising the State to participate in and agree to amendments of the Treaties which are within the original scope and objectives of the Treaties. It is the opinion of the Court that the first sentence in Article 29, s. 4, sub-s. 3 of the Constitution must be construed as an authorisation given to the State not only to join the Communities as they stood in 1973, but also to join in amendments of the Treaties so long as such amendments do not alter the essential scope or objectives of the Communities. To hold that the first sentence of Article 29, s. 4, sub-s. 3 does not authorise any form of amendment to the Treaties after 1973 without a further amendment of the Constitution would be too narrow a construction; to construe it as an open-ended authority to agree, without further amendment of the Constitution, to any amendment of the Treaties would be too broad. (para. 6)" The plaintiff made four arguments challenging the constitutionality of the 1986 Act. These were: The Court rejected all of these arguments. They noted that the Treaty of Rome provided for moving from unanimous voting to qualified majority and concluded that: "The Community was thus a developing organism with diverse and changing methods for making decisions and an inbuilt and clearly expressed objective of expansion and progress, both in terms of the number of its Member States and in terms of the mechanics to be used in the achievement of its agreed objectives. (para. 13)" The Court ruled further that the "new" policy areas fell within the original objectives of the Treaty of Rome, that the creation of a new court would not increase the judicial power already delegated to the European institutions, and that the Plaintiff had failed to show how the new powers to be granted to the Council of Ministers could threaten constitutional rights.

Part III of the Single European Act

Walsh and Henchy JJ. gave separate judgements with which Hederman J. concurred. They ruled that were Ireland to ratify Part III it would amount to unconstitutional delegation of the state's external sovereignty. They rejected the argument that the constitutionality of a treaty could only be questioned when it was incorporated into law by a statute and ruled that the courts had the power to interfere in the government's exercise of foreign affairs in the case of there being a "clear disregard by the government of the powers and duties conferred on it by the Constitution." The Court's dissenting members argued that the courts had no jurisdiction to question the constitutionality of a treaty which had not been incorporated into the law of the state. While they agreed with the majority that the courts could interfere with the government's exercise of the state's foreign affairs in the case of a clear disregard of the Constitution, they did not agree that the government had shown any such disregard.