Slovenian European Union and NATO membership referendum, 23 March 2003, 89.6% in favour, turnout 60.2% — 2003 Hungarian European Union membership referendum, 12 April 2003, 83.8% in favour, turnout 45.6% — 2003 Lithuanian European Union membership referendum, 10–11 May 2003, 91.9% in favour, turnout 63.4% — 2003 Slovak European Union membership referendum, 16–17 May 2003, 93.7% in favour, turnout 52.1% — 2003 Polish European Union membership referendum, 7–8 June 2003, 77.5% in favour, turnout 58.9% — 2003 Czech European Union membership referendum, 13–14 June 2003, 77.3% in favour, turnout 55.2% — 2003 Estonian European Union membership referendum, 14 September 2003, 66.8% in favour, turnout 64.1% — 2003 Latvian European Union membership referendum, 20 September 2003, 67.5% in favour, turnout 71.5% Since the results were in favourable in all cases, all ten candidate countries were admitted as members of the EU, acceding on 1 May 2004. Euro Denmark and the United Kingdom received opt-outs from the Maastricht Treaty and do not have to join the euro unless they choose to do so; Sweden has not received an opt-out, yet deliberately does not live up to the requirements for joining. Two referendums have been held on the issue, both of which rejected accession. — 2000 Danish euro referendum, 28 September 2000, 53.2% against, turnout 87.6% — 2003 Swedish euro referendum, 14 September 2003, 55.9% against, turnout 82.6% European Constitution, 2005 Several member states used or intended to use referendums to ratify the Treaty establishing a Constitution for Europe (TCE). — 2005 Spanish European Constitution referendum, 20 February 2005, 81.8% in favour, turnout 41.8% — 2005 French European Constitution referendum, 29 May 2005, 54.7% against, turnout 69.4% — 2005 Dutch European Constitution referendum, 1 June 2005, 61.5% against, turnout 63.3% — 2005 Luxembourgian European Constitution referendum, 10 July 2005, 56.5% in favour, turnout 90.4% Referendums were planned, but not held, in: — Czech European Constitution referendum — Danish European Constitution referendum — Irish European Constitution referendum — Polish European Constitution referendum — Portuguese European Constitution referendum — United Kingdom European Constitution referendum Treaty of Lisbon Only one member state, Ireland, obliged by their constitution, decided on ratification of the Treaty of Lisbon through a referendum. — a referendum to approve the Twenty-eighth Amendment of the Constitution Bill, 2008 (Ireland), 12 June 2008, 53.2% against, turnout 53.1% In 2008, Irish voters rejected the Treaty of Lisbon. — a referendum to approve the Twenty-eighth Amendment