A lobby group in favour of the current MMP voting system wants the Government to introduce rules it says would prevent big business hijacking the debate about whether to change it.
The group Campaign for MMP says the Government is due to announce its plans for a referendum on the issue within the next fortnight.
The referendum will take place at next year's general election, and if a change is wanted, people will be asked to vote for MMP or an alternative in another referendum during the 2014 election.
Campaign for MMP says big business used vast amounts of money in a failed attempt to oppose the system's introduction in the 1990s.
The group says the Government should introduce a spending cap on lobbying leading up to the referenda, so a fairer debate can take place.
Peter Shirtcliffe, who led the earlier failed campaign, is now co-founder of the group Put MMP to the Vote.
He says the two upcoming referenda could be held closer together, so any change could be in place for the 2014 general election.
