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.
According to the Portuguese Constitution, the result of the referendum is binding if more than of half of registered voters turn out.
The text was to have been revised in June 2005 with the express purpose of allowing the referendum to be held on the same day as the municipal elections.
The referendum was initially scheduled for April 2005 using the question "Do you agree with the Charter of Fundamental Rights, the rule of qualified majority voting and the new institutional framework of the EU, as defined by the European Constitution?
However, in December 2004, the Constitutional Court of Portugal rejected the proposed question, deeming it unclear.