This issue has become increasingly important in debates over the role and future of the European Union (EU) since reference to respect for fundamental rights was included in the Treaty on European Union (TEU) in 1993 and later expanded by the Treaty of Amsterdam (1997), which declared the EU to be founded on respect for human rights and fundamental freedoms. The rights themselves are not explicitly listed anywhere in the EU's treaty base. Instead, reference is made to the European Convention on Human Rights (formally the Convention for the Protection of Human Rights and Fundamental Freedoms), adopted by the Council of Europe in 1950, and to the constitutional traditions of the EU Member States. This has not prevented the drawing up in 2000 of a Charter of Fundamental Rights of the European Union. Nor has it prevented the EU in its external relations from making respect for human rights a precondition for closer ties and, indeed, membership. The EU has not, however, signed the European Convention on Human Rights, the European Court of Justice ruling in 1996 that it did not have the competence to do so. That human rights enjoy an increasingly higher profile in the EU is underlined by the fact that a Member State's suspected breach of them may be investigated. Ultimately its voting rights, as well as other rights deriving from the TEU and Treaty of Rome (1957), may be suspended where a serious and persistent breach is confirmed. The case law of the Court of Justice of the European Union recognizes the principles laid down in the European Convention on Human Rights. This respect for human rights was confirmed by the Member States in the preamble to the 1986 Single European Act and later incorporated into Article 6 (former Article F) of the TEU, which is based on the above Convention and the shared constitutional traditions of the Member States. The guarantee of respect for fundamental rights has been further strengthened by the Treaty of Amsterdam, which has extended the jurisdiction of the Court of Justice to cover respect for the rights deriving from Article 6 with regard to action by the EU institutions. See: Charter of Fundamental Rights of the European Union; European Convention on Human Rights (ECHR)