The right to "veto" laws in the EU - even if all other member states are in favour.
In June 1965, the French President Charles de Gaulle began a boycott of all Council meetings - the "empty chair crisis".
Under the Treaty of Rome, 1957, agricultural and budget issues were to be determined by majority decision-making after a transition period during which they would be decided by unanimously. At the end of the transition period De Gaulle refused to accept the abolition of unanimity voting, and so began a French boycott.
By January 1966 a compromise was found allowing member states to veto decisions they regarded as "a vital national interest". Vital interests are important interests, but in reality the Luxembourg compromise could be used in any area as long as a blocking minority supported the vetoing country.
The compromise worked in the way that a state invoking the right of veto was supported by the states in favour of the right of veto, who would then let the negotiations continue. The Luxembourg compromise had no legal status, but was a political agreement expressed in a "communiqué" referring to disagreements between France and the five other founding member states of the EEC.
Despite this the compromise was abided by until December 1985 when the presidents and prime ministers of the member states agreed to forget it and allow each other to deny they had agreed to forget it.
People may thus stiill disagree as to whether the right of veto introduced in the Luxembourg compromise still exists today. The answer is that it only exists when respected by states with a blocking minority of votes and it has not been used since 1984.
The political veto right, referred to as the Luxembourg compromise, should not be confused with the veto right that each EU member state has when unanimity is required for making na EU law or taking some other decision.
The Lisbon Treaty has abolished the Luxembourg compromise by introducing the "ordinary legislative procedure" and a new "Ionnanina compromise".
Any exception from majority-voting in the Council and the Parliament's right of co-decision must thus be explicitly allowed. The only derogation may be the so-called "Ioannina compromise" now inserted by Poland in Prorocol number 9 and a special Declaration. This clause will not change the voting rules.
The former right-hand man of Jean Monnet, Georges Berthoin, proposed to re-establish the veto right in vital questions by demanding that a prime minister should be obliged to defend a veto at an EU summit.
This proposal has been circulated by the Democracy-Forum group in the Convention on the Future of Europe, with the additional demand that the exercise of the veto must also be decided by the respective national parliament in a public debate.
Europa glossary http://europa.eu/scadplus/glossary/luxembourg_compromise_en.htm