Constitutional practicability of referendum on EU Constitution

Yes. Binding referendum expressly on international treaties provided.

Approval of transfer of sovereignty without effect of constitutional amendment

Majority of votes from parliament, Art. 166 V, 161 lit. i, 116, 168 ConstPortugal. On proposal of the parliament or the government a referendum is provided for on matters of national interest which is expressly the approval of an international convention, Art. 115 I, III, 161 lit. j, 197 I lit. e ConstPortugal.

Approval of transfer of sovereignty with effect of constitutional amendment

Not expressly regulated, but constitutional amendment required.

Approval of constitutional amendment

Majority of 2/3 from members of parliament, Art. 286 I ConstPortugal. Limit of the amendment are the fundamental principles of the constitution, Art. 288 ConstPortugal.

Other constitutional regulations about referendums

Initiatives and referenda provided for, Art. 115, 167 ConstPortugal.