Constitutional practicability of referendum on EU Constitution

Yes. Binding referendum provided if constitutional amendment, a total revision or an amendment of fundamental principles of the constitution effected. Otherwise binding referendum requires implementation by constitutional amendment. Consultative referendum expressly provided. Exclusion of international affairs only for initiatives, not for referendums.

Approval of transfer of sovereignty without effect of constitutional amendment

Majority from both chambers, Art. 94 ConstSpain.

Approval of transfer of sovereignty with effect of constitutional amendment

Previous amendment of the constitution required, Art. 95, 94 ConstSpain.

Approval of constitutional amendment

Majority of 3/5 from both chambers. If this majority cannot be reached a committee drafts a new text which can be approved by majority of 3/4 from the members of parliament and the majority of the members of the senate, Art. 167 ConstSpain. Referendum on the constitutional amendment is required if demanded by 1/10 from the members of one of the chambers , Art. 167 III ConstSpain. In case of a total revision of the constitution or the amendment of fundamental principles of the constitution both chambers have to approve with a majority of 3/4 before and after a disbandment and re-election of both chambers. Additionally a referendum on the constitutional amendment required, Art. 168 ConstSpain.

Other constitutional regulations about referendums

Initiatives and referenda can be held but internatational affairs are expressly excluded, Art. 87 III ConstSpain. Consultative referenda can be held on political decisions of far-reaching consequences by proposal of the prime minister approved by the parliament, Art. 92 ConstSpain.