An early public information campaign about the MMP referendum is essential or it will risk being hijacked by the mania of the Rugby World Cup, a select committee has heard.

The electoral legislation committee is hearing submissions on next year's referendum, which will ask New Zealanders if they want to retain MMP or move to a different system.

If a majority want to change, a second referendum in 2014 will ask voters to choose between MMP and the most popular of four alternatives. If the alternative wins a majority, it will take effect for the 2017 election.

The Campaign for MMP urged the committee yesterday to recommend a comprehensive public information campaign that started early. "It is crucial that we have a well-informed, well-funded information campaign ... as early as we can in 2011," said spokeswoman Sandra Grey, a politics lecturer at Victoria University. "This reflects the fact that there is a possibility that the election may be before the Rugby World Cup or just after it, not allowing much time for public information because people would be concentrating on the rugby."

The Rugby World Cup runs from September 9 to October 23 next year.

Dr Grey also stressed the importance of spending caps on advertising for the referendum to ensure a level playing field.

Campaign members had gone through submissions to the committee and found that 80 per cent recommended spending caps.

The current bill contains no limit on advertising spending for the referendum. Dr Grey suggested a cap of $350,000.

"We don't think freedom of speech is about allowing everyone freedom to spend on advertising and to spend freely on advertising."

Challenged on how a spending cap could be administered, she said it would be best for it to apply to campaigning for each option: Mixed-Member Proportional, First Past the Post, Preferential Voting, Single Transferable Vote and Supplementary Member.

She conceded it would be much harder to have a cap of $350,000 per group or individual, as a group could simply splinter into smaller groups if it wanted to spend more.

As a compromise, she suggested banning broadcasting advertising, and using television only as a platform for the public information campaign.

"TV and radio are most susceptible to big-spending, manipulative advertising campaigns. The crucial concern of submitters is that the big-business-funded lobbies should not be able to buy their preferred electoral system as they nearly succeeded in doing in the 1993 electoral referendum."

If MMP is changed, it will happen in three stages:
* 2011: Referendum on keeping the present system.
* 2014: If a majority want change, a second referendum will ask which of five systems is supported.
* 2017: If an alternative to MMP is the popular choice, it will come into effect in the general election.