Article 167
1. Bills on Constitutional amendment must be approved by a majority of three-fifths of the members of each House. If there is no agreement between the Houses, an effort to reach it shall be made by setting up a joint Commission of Deputies and Senators which shall submit a text to be voted on by the Congress and the Senate.
2. If approval is not obtained by means of the procedure outlined in the foregoing clause, and provided that the text has been passed by an absolute majority of the members of the Senate, Congress may pass the amendment by a two-thirds vote in favour.
3. Once the amendment has been passed by the Cortes Generales, it shall be submitted to ratification by referendum, if so requested by one tenth of the members, of either House within fifteen days after its passage.
