Legal provisions for optional referendums at national level

Portugal
Constitution (7th revision, 2005)
Article 115 (Referenda)
1. Upon a proposal submitted by the Assembly of the Republic or the Government in relation to matters that fall within their respective competences, in the cases provided for and as laid down in the Constitution and the law, the President of the Republic may decide to call upon citizens who are registered to vote in Portuguese territory to directly and bindingly pronounce themselves by referendum.
2. Referenda may also result from the submission by citizens of an initiative to the Assembly of the Republic. Such initiatives shall be submitted and considered under the terms and within the time limits laid down by law.
3. Only important issues concerning the national interest which the Assembly of the Republic or the
Government must decide by approving an international convention or passing a legislative act may be the object of a referendum.
4. The following are excluded from the scope of referenda:
a) Amendments to the Constitution;
b) Questions and acts with a budgetary, tax-related or financial content;
c) The matters provided for in Article 161 of the Constitution, without prejudice to the provisions of the following paragraph;
d) The matters provided for in Article 164 of the Constitution, except for the provisions of subparagraph (i).
5. The provisions of the previous paragraph do not prejudice the submission to referendum of important issues concerning the national interest that must be the object of an international convention pursuant to Article 161(i), except when they concern peace or the rectification of borders.
All issues of national importance (except those ruled out by Articles 115(4) and 115(5)) can be subject to an optional referendum.