Constitutional practicability of referendum on EU Constitution

Yes. Binding referendum expressly provided for transfer of sovereignty but requires enactment by constitutional law. Consultative referendum can anyhow be held if ordered by ad-hoc-law.

Approval of international treaties without transfer of sovereignty

Majority of votes from both chambers, Art. 49, 39 II ConstCzRep.

Approval of transfer of sovereignty without effect of constitutional amendment

Majority of 3/5 from members of parliament and 3/5 of the votes from senate, Art. 10a I, 39 IV ConstCzRep. With constitutional law a referendum can be ordered, Art. 10a II ConstCzRep.

Approval of transfer of sovereignty with effect of constitutional amendment

Previous constitutional amendment required if constitutional court decides that an international treaty is not in conformity with the constitution, Art. 89 III, 87 II ConstCzRep.

Approval of constitutional amendment

Only by constitutional act that requires a majority of 3/5 from members of parliament and 3/5 of the votes from senate, Art. 9 I, 39 IV ConstCzRep.

Other constitutional regulations about referendums

With constitutional act referenda can be implemented into constitution with a majority of 3/5 from the members of parliament and 3/5 of the votes from senate, Art. 2 II ConstCzRep.