The term ‘unanimity’ relates to the requirement for all EU countries when meeting within the Council to be in agreement before a proposal can be adopted.
The Single European Act, signed in 1987 amended the Treaty of Rome to add new momentum to European integration and to complete the internal market. It reduced the number of policy areas for which unanimity was required in order to adopt legislation.
Nevertheless, a limited number of policies judged to be sensitive remain subject to unanimity voting: taxation, social security or social protection, the accession of new countries to the EU, foreign and common defence policy and operational police cooperation between EU countries.
Source: EUR Lex Glossary