ACT leader John Banks says he won't support any changes to MMP and he particularly doesn't like the proposed abolition of the "coat tails" rule.
It was the one seat threshold rule that got him into parliament at the last election - National backed him to win Epsom hoping he would bring in extra MPs and it would have a strong partner party.
The rule is that if a party wins an electorate seat it gains MPs in proportion to its party vote, without having to reach the five per cent threshold other parties must reach if they don't win an electorate.
Mr Banks won Epsom but ACT gained only one per cent of the party vote - not enough for any more MPs.
The Electoral Commission proposes abolishing the rule and making all parties reach a four per cent threshold.
That means it is highly unlikely National will again back Mr Banks - unless ACT is able to significantly increase its poll rating between now and 2014, which it is showing no sign of achieving.
"The Electoral Commission's paper on this issue is woeful," Mr Banks said on Monday after the commission had released its proposals.
"It uses the weight of partisan submissions to justify removing the one seat threshold... none of the proposals offer any additional benefits to New Zealand."
The commission says most of the more than 4700 public submissions it received wanted the one-seat threshold abolished, and its own opinion is that the rule is unfair on other parties.
The Green Party is welcoming the proposals and says the level of public participation in the review process was "fantastic".
"Removing the one electorate seat threshold will make a big difference for fairness by making sure that the votes of people in some electorates are not given more weight than others," electoral reform spokeswoman Holly Walker said.
The Conservative Party, which won 2.6 per cent of the party vote last year but didn't gain any seats, also likes the proposals.
"While our expectation is that we would have crossed the five per cent threshold at the next election, we nonetheless welcome the commission's recommendation to lower it," party leader Colin Craig said.
The right-wing Maxim Institute opposes the proposals, saying lowering the threshold will make it easier for small parties to get into parliament and harder for governments to be formed.