Issues of sub-national referendums regulated at the national level

Saint Kitts and Nevis
Federation of Saint Kitts and Nevis Constitutionalorder of 1983
(Adopted in June 22, 1983)
http://pdba.georgetown.edu/constitutions/kitts/kitts83.html
Article 113.
(1)The Nevis Island Legislature may provide that the island of Nevis shall ceaseto be federated with the island of Saint Christopher and accordingly that thisConstitution shall no longer have effect in the island of Nevis.
(2)A bill for the purposes of subsection (1) shall not be regarded as being passedby the Assembly unless on its final reading the bill is supported by the votesof not less than two-thirds of all the elected member of the Assembly and sucha bill shall not be submitted to the Governor-General for his assent unless[…]
b)after it has been passed by the Assembly, the bill has been approved in areferendum held in the island of Nevis by not less than two-thirds of all thevotes validly cast on that referendum;
Subnationalreferendums regulated at the national level are provided on the issue ofsecession.