They might not agree on much, but the two lobby groups on opposing sides of last year's MMP referendum have spoken in unison.

The pro-MMP Campaign for MMP and the anti-MMP Voters for Change had a simple but blunt message: don't let the politicians make the changes they want or block the ones they don't want.

Bad enough that the review bars the commission from considering two of the major components of the system - Maori representation and the size of Parliament.

Preventing the commission from canvassing the size of Parliament is ludicrous, given the MMP review is charged with solving the looming dilemma of keeping Parliament proportional as the population grows.

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That aside, the commission's purview still covers a number of aspects of MMP where change would likely not be to the liking of political parties.

These include whether to ban so-called "dual candidacy" where candidates who lose electorate contests get into Parliament by virtue of a high list placing; whether list MPs should be able to contest byelections; whether to introduce open lists which would see voters rather than parties ranking the candidates; and whether the one-seat threshold which saw Act get five MPs into Parliament in 2008 by virtue of winning the Epsom electorate should be canned.

The good news is that the commission's review looks like being far more rigorous and authoritative than the limp effort conducted by a parliamentary select committee back in 2001, which left people feeling short-changed.

That committee's report produced nothing in the way of major recommendations because its members from parties across Parliament could not reach unanimity on a range of matters.

Former Justice Minister Simon Power - who wrote the law triggering the review if MMP was retained in the 2011 referendum - deserves credit for realising the 2001 review was a debacle.

The commission deserves credit for the way it is conducting the review. Yesterday it released a consultation paper as the first basis for public submissions.

Once those have been considered, it will then put out a proposals paper for further public submission before making its final recommendations to Justice Minister Judith Collins by the end of October.

The process - to be backed up by a $1.6 million budget to be spent on advertising and market research - will ensure its recommendations carry significant weight.

They will have to do so to force change. Otherwise, they could fall foul of political bickering or obstruction.

The determining factor will be how deeply the public engages with the exercise.

It is now up to voters to say what they want and do not want in MMP. And not least because this may be their last chance to do so for some time.