A group lobbying to keep the MMP voting system launched its campaign in Auckland on Friday.
Keep MMP formed last year to encourage voters to support retaining the status quo the referendum to be held on the same day as the general election, 26 November.
It will ask voters whether they want to keep MMP and, if there was a change, which of four other voting systems they would choose.
The alternative systems are: First Past the Post, Preferential Voting, Single Transferable Vote and Supplementary Member.
Keep MMP is also holding a nationwide MMP Day on Saturday, with events from Whangarei to Dunedin.