 However, the Lisbon treaty was approved by Irish voters when the Twenty-eighth Amendment of the constitution was approved in the second Lisbon referendum, held in October 2009.The Treaty of Lisbon was signed by the member states of the European Union on 13 December 2007.It was in large part of a revision of the text of the Treaty establishing a Constitution for Europe after its rejection in referendums in France in May 2005 and in the Netherlands in June 2005.