Legal provisions for mandatory referendums at national level

Viet Nam
Answer
No
Source
1992 Constitution of the Socialist Republic ofVietnam
(adopted in 9 November 1946 , amended in 25December 2001)
http://www.na.gov.vn/htx/English/C1479/?cateid=1479#isSI4SFeT3Hz
Comment
Constitution provides only for optional referendum.