Voters unhappy with the ACT Party's problems can choose to improve the MMP electoral system at a referendum next year, a pro-MMP group says.
There will be a referendum on MMP at the same time as the next election, when voters will be asked whether they want to change to another system.
Prime Minister John Key said yesterday he thought "the ACT debacle" would affect voter attitudes.
"I think it will increase the likelihood that people will vote MMP out," he said.
"I'm wondering whether the public might say 'look, very small parties are consuming quite a lot of time' and maybe they will take the view that MMP fundamentally isn't working so well."
Campaign for MMP spokeswoman Sandra Grey said voting for MMP would trigger a thorough review of it.
"Concerns people have can be fixed in the review of MMP that the Government has already committed to if a majority of people back MMP in 2011."
The best way to improve MMP was to vote for it, she said.
"It is time to look at how MMP is working, but that doesn't mean we should throw the baby out with the bath water."
ACT has been hit by the resignation of disgraced MP David Garrett, and party leader Rodney Hide's judgment is being questioned.
Mr Key reiterated his opinion that Mr Garrett should quit Parliament altogether.
Mr Garrett resigned after telling Parliament last week he used a dead baby's identity to obtain a false passport 26 years ago, which Mr Hide knew about before Mr Garrett became an MP in 2008.
He was prosecuted for that offence in 2005, and was discharged without conviction.