Who can initiate an optional referendum at the national level?

The Constitution of the Republic of Namibia (adopted in 1992)

Article 63(2). The National Assembly shall further have the power and function, subject to this Constitution:

g) to initiate, approve or decide to hold a referendum on matters of national concern;

Article 132(3a) Notwithstanding the provisions of Sub-Article (2) hereof, if a bill proposing a repeal and/or amendment of any of the provisions of this Constitution secures a majority of two-thirds of all the members of the National Assembly, but fails to secure a majority of two-thirds of all the members of the National Council, the President may by Proclamation make the bill containing the proposed repeals and/or amendments the subject of a national referendum.

In the case of issues of national importance, the law does not specify whether minority or majority of the legislature should approve a referendum.