The European Parliament has called on member states to hold simultaneous referendums on the new European Union Constitution.
Some EU member states will not be holding a referendum
MEPs urged all 25 states to organise their ratification of the treaty between 5 and 8 May next year.
The new constitution agreed by 25 EU leaders in June must win approval in each member state, either by a vote in parliament or by public referendum.
The first referendum is expected to be held in Spain on 20 February.
MEPs chose the May dates because of the "symbolic" value.
French MEP Thierry Cornillet, who proposed the motion, said: "The European Union has the opportunity to build its future on a very strong symbolic platform - the 60th anniversary of the end of the war (World War II) that led to its birth."
But the UK MEP Timothy Kirkhope, the Conservative party's European Parliament
spokesman on constitutional affairs, resented being told when to hold a referendum.
"This is a matter for the British Parliament and other national governments to decide on," he said.
"It is not for the European Parliament to tell countries when the referendums should be held."
Other countries which say they will hold a referendum are: France, Ireland, the Netherlands, Portugal, Luxembourg, Spain, the Czech Republic and Denmark.
Others have decided to hold a vote in parliament, while some are still undecided.
The EU constitution sets out the powers of the national governments of the member states and the EU's various institutions, and includes a charter of fundamental rights.