Issues of sub-national referendums regulated at the national level

Uzbekistan
Answer
Creation/merger/abolition of sub-national territories
Source
Constitution 1992
Article 74. The Republic of Karakalpakstan shall have the right to secede from theRepublic of Uzbekistan on the basis of a nation-wide referendum held by thepeople of Karakalpakstan.
http://www.gov.uz/en/constitution/