The Portuguese referendum on the Treaty establishing a Constitution for Europe was a planned referendum to be held on October 9, 2005 to decide whether the Portugal should ratify the proposed Constitution of the European Union. On 12 March 2005, the Prime Minister José Sócrates said that he would seek to have the Constitution of Portugal amended to allow that a referendum be held on October 9, 2005 alongside the municipal elections taking place at that time. The agreement between the two main parties was made on 1 June 2005.