Issues excluded from being the subject of referendums at the national level

Constitution of Croatia 2010

http://www.proyectos.cchs.csic.es/europeconstitution/sites/proyectos.cchs.csic.es.europeconstitution/files/CONSTITUTION_CROATIA_0.pdf  

Referendum Law

http://www.zakon.hr/z/359/Zakon-o-referendumu-i-drugim-oblicima-osobnog-sudjelovanja-u-obavljanju-dr%C5%BEavne-vlasti-i-lokalne-i-podru%C4%8Dne-(regionalne)-samouprave

No issuesare explicitly excluded from being the subject of national referendums.