To encourage closer cooperation between European Union (EU) countries which wish to go further than the degree of integration provided for by the Treaties (in the fields of social affairs, elimination of border controls, etc)., various instruments have been introduced, such as the Social Policy Agreement and the Schengen Accords. This has allowed Member States who so wish to make progress at a different pace or on different objectives outside the institutional framework of the EU. After the Treaty of Amsterdam came into force in 1999, the use of these instruments was put on a more formal footing with the introduction of the concept of closer cooperation in the Treaty on European Union (EU Treaty) and the Treaty establishing the European Community (EC Treaty).The aim of such cooperation is to enable a limited number of Member States that are willing and able to advance further to deepen European integration within the single institutional framework of the EU. Closer cooperation must meet a number of conditions. In particular, it must: cover an area that does not fall within the exclusive competence of the Community; be aimed at furthering the objectives of the EU; respect the principles of the Treaties and the Community acquis; be used only as a last resort; involve a minimum number of Member States; allow the gradual integration of other Member States. Closer cooperation under the EC Treaty is authorized by the Council, acting by a qualified majority on a proposal from the Commission and after consulting the European Parliament. The object of closer cooperation under the EU Treaty, according to the provisions of the Treaty of Amsterdam, is to develop the area of freedom, security and justice. At the request of the Member States concerned, this is authorized by the Council, acting by a qualified majority after both obtaining the European Commission's opinion and following submission of the request to the European Parliament. According to the Treaty of Amsterdam, a Member State can always refuse to allow closer cooperation in a particular area for reasons of national political importance. However, a qualified majority in the Council can refer the matter to the European Council, which must act unanimously. The Treaty of Nice aimed, in particular, to simplify the use of closer cooperation and introduced significant changes: the minimum number of Member States required for closer cooperation has been cut by a half (Treaty of Amsterdam) to eight, irrespective of the total number of Member States; Member States can no longer prevent closer cooperation. The matter may be referred to the European Council, but it is the Council of Ministers that decides by the majority provided for in the Treaties; under the EC Treaty, Parliament's assent is required if closer cooperation covers a field subject to codecision; an additional condition for the implementation of closer cooperation has been added: it must not jeopardize the internal market or economic and social cohesion. The Treaty of Nice introduced the possibility of closer cooperation in the field of the common foreign and security policy, except for matters having military or defence implications. At procedural level, decisions are taken by the Council, after an opinion from the Commission, acting by qualified majority on the basis of a common strategy. See: Social Policy Agreement; Treaties