The Government and lobby groups are urging people to have their say on MMP through the Electoral Commission's review of the system.
A referendum held at the same time as last November's election showed a clear majority for retaining MMP and the commission is bound by law to review it.
The review was launched on Monday and key parts of the voting system could be changed before the next election in 2014.
Justice Minister Judith Collins says it's a great opportunity for public input into how the system works.
"I strongly encourage all New Zealanders to take part and have their say in this important process, and to suggest any improvements they'd like to see," she says.
The organisation that supported MMP in the run-up to the referendum, Campaign for MMP, says it knows many people want to change parts of it and they should put in their submissions.
Voters for Change, which opposes MMP, says "broad discussions" are needed on how to change it.
It wants to scrap parts of it and change others.
Maori representation and the number of seats in Parliament are the only issues outside the scope of the review.
The most controversial parts of MMP are the threshold parties have to reach to get seats in parliament, the way they can get around it by winning an electorate seat, and the way MPs who lose their electorate seats can get back in on party lists.
Another peculiarity is that electoral law currently allows list MPs to stand in by-elections, and there have been cases where most of the candidates were already list MPs.
The commission is inviting written submissions and will hold public meetings.
It will give its recommendations to the Government in October.
Parliament will make the final decisions with law changes in place before the next election.
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