Lowering the MMP threshold to 4% would create "instability" and chaos", Winston Peters says ahead of the first set of proposals to be released since a review on the voting system began.
Tomorrow will see the Electoral Commission publish findings following nearly a year of public consultation on the MMP system.
The New Zealand First leader told Q+A this morning he opposes lowering the vote threshold from 5% to 4%, which would enable more minority parties a voice in Parliament.
"We're talking about a compromise between democracy and stability.
"If you start lowering the threshold and allowing this coat-tailing to go on, you'll actually destroy stability, and that's not what the public want."
Peters said if MPs were good enough they should be able to make 5% of the vote.
However, Mana leader Hone Harawira supported a change in the law because it would encourage more people to vote.
"The higher the threshold, the more people start thinking that, 'this is not something that really matters, so I'm not going to bother'.
"And that's why New Zealanders don't bother to vote," Harawira said.
Coat-tailing - which has allowed The Act party and United Future to bring in extra MPs on the back of a win in an electorate seat - is also expected to go as a quid pro quo in the review.
Labour MP Lianne Dalziel agreed with lowering the threshold, but said the law for coat-tailing should "go completely".
"From the 2008 general election where we saw a party that got just over 3.5% of the vote getting four MPs on the coat tails of the leader of the Act party and Winston Peters."
Harawira agreed coat-tailing needed to change considerably.
The review of MMP arose after the 2011 Referendum on the voting system, held alongside the General Election on November 26, when the majority of voters chose to keep MMP as New Zealand's voting system.
An independent review of MMP has since been conducted by the Electoral Commission, which allowed members of the public to submit their views on the subject.
The closing date for submissions was in May, and since then the commission has been reviewing the findings, and will tomorrow release a proposal paper based on these.
The public will again be asked to comment on the proposal paper, and a final paper will be presented to the Minister of Justice in October.