At its campaign launch in Gisborne on Sunday, Te Pāti Māori asked its supporters for something no party had requested so openly before: candidate votes for the party, party votes for its allies on the left.

The request rests on MMP’s overhang rule. A party that wins more electorates than its party vote covers keeps them all, and Parliament grows.

Te Pāti Māori expects to win its seats through the Māori electorates alone, so its party votes can be given away. On current polling, that manoeuvre is worth three or four bonus seats for the left block.

This tactical manoeuvre makes political sense, it is legal, and that is exactly the problem.

For thirty years, every party knew about the possibility of gaming MMP through creating an overhang. No party tried to engineer it for fear of voter backlash. Until Sunday.

The problem is not just the overhang that Te Pāti Māori’s move will create. It will also encourage other voters to retaliate. And indeed, if centre-right voters did that, the distortion would be even bigger.

On current polling, National will win more electorates than its party vote covers. Effectively, this would leave close to 900,000 National party votes with no effect whatsoever on the result.

In our new research note, we model what happens under such a scenario. If one National party vote in nine moved to a coalition partner, the Government would gain a parliamentary majority even if the opposition wins more votes in total.

Such an outcome would be deeply ironic. New Zealand adopted MMP after first-past-the-post elections in which the party with the most votes still lost the election. That was not supposed to happen anymore.

Prime Minister Christopher Luxon has promised a referendum on MMP if re-elected. Right now, however, there is little public appetite for change. That would clearly change if tactical voting reversed the outcome of the 2026 election.

It did not have to come to this. Back in 2012, the Electoral Commission recommended some fixes to MMP which would have solved the overhang problem. Unfortunately, none of the Commission’s proposals were implemented.

Te Pāti Māori should reconsider its position on openly encouraging tactical voting. Because if they do not, it would only provoke other voters to do the same.

The result could not only be a government without popular support but also the end of MMP as New Zealand’s electoral system.

Read our research note ‘Unravelling MMP’ and listen to Oliver and Nick discuss these issues on our podcast.