2005 French European Constitution referendum
A referendum on the Treaty establishing a Constitution for Europe was held in France on 29 May 2005 to decide whether the French government should ratify the proposed constitution of the European Union. The result was a victory for the "no" campaign, with 55% of voters rejecting the treaty on a turnout of 69%.
Source: Wikipedia — 2005 French European Constitution referendum (CC BY-SA 4.0)