Article 138

Laws amending the Constitution and other constitutional laws shall be adopted by each House by means of two successive decisions taken at intervals of not less than three months, and shall be approved by an absolute majority of the members of each House on the second vote. The said laws shall be submitted to a popular referendum if so requested within three months of their publication by one fifth of the members of a House or five hundred thousand voters or five Regional Councils. A law submitted to a referendum shall not be promulgated unless it is approved by a majority of valid votes. No referendum shall be held if the law has been approved on the second vote by each of the Houses with a majority of two thirds of its members.