Anti-MMP lobby group Vote for Change says deals between parties over the Epsom and Ohariu electorates are a good reason to get rid of the mixed member proportional voting system.
Strategic manouevres by political parties are coming under scrutiny as Epsom constituents wait to see whether the National Party will endorse ACT candidate John Banks.
National's candidates in Ohariu and Epsom are running a party vote only campaign.
In the last election, candidates for United Future and ACT won those seats and went on to support National in government.
In the case of ACT, by winning Epsom it got its full share of five seats in Parliament from the 3.65% of the party vote it received, while New Zealand First, which had a larger party vote but did not win an electorate, got no seats.
Vote for Change spokesperson Jordan Williams says it's a quirk of MMP that it allows backroom deals to be embedded in the system.
He says parties can coat-tail off electorate seats giving disproportionate outcomes to what is supposed to be a proportional system.
"We have small parties with that 5 - 10% ... having a huge amount of influence and being able to ensure that National and Labour are bidding for their support."
Mr Williams supports the alternative Supplementary Member (SM) voting system in which there are two votes. There would be 90 electorate seats and the remaining 30 supplementary seats would be allocated on the party vote.
"Under Supplementary Member, the list MPs are entirely determined by the party vote and the electorates are entirely determined by the results in those electorates.
"You'd have every party wanting party votes, as well as electorate votes."
However Sandra Grey from the group Keep MMP said political deals are part of any voting system.
She said history shows that since MMP was introduced in 1996, if people haven't liked deals being done they have used their vote to express this.
Ms Grey said people at an Epsom candidates meeting she attended recently said they were going to vote for the party and candidate they wanted.
Victoria University assistant law lecturer Kate Stone says systems other than MMP can be manipulated, and points out that if voters opt to keep MMP a review is planned in 2012.
A senior lecturer in political studies at the University of Auckland, Jennifer Curtin, says a review might look at whether to keep the one seat threshold and the quota threshold, so a proportional element may be retained but the skewed effect in certain electorates removed.
For more on the voting systems go to Radio New Zealand's Referendum page.