New states and boundary adjustment, etc
Section 8(1)(b) · 1999 Constitution (2004 edition)
What Constitution says
(b) a proposal for the creation of the State is thereafter approved in a referendum by at least two-thirds majority of the people of the area where the demand for creation of the State originated;
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 22–24. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections