Next time New Zealand goes to the polls, Kiwis might be faced with more than just deciding the next Government.

Referenda on recreational marijuana use, euthanasia and the MMP system of governance itself might be left in voters' hands in 2020.

Justice Minister Andrew Little told RadioLIVE on Monday he's considering rolling them altogether into "one big series of referenda at the next general election".

Only the referendum on recreational marijuana use was agreed to in coalition negotiations. The vote on ACT leader David Seymour's End of Life Choice Bill wasn't originally going to involve a public vote, but Mr Seymour agreed to it in order to get New Zealand First's vote in Parliament.

"I've been talking to him about the mechanics of that," said Mr Little, who said they hope to have a confirmed date for the recreational marijuana referendum "hopefully in the next two or three weeks".

To get the Green Party's support in forming their coalition, Labour and NZ First agreed to hold a referendum before or at the 2020 election.

With those two referenda on the cards, Mr Little says they might as well tackle MMP while they're at it, even though it wasn't signalled during the election campaign, nor agreed to in coalition negotiations.

"It has been hanging around. The previous Government, it hit their desk and they decided not to do anything about it. If we don't do anything about it, it'll come up again as it periodically does at some point in the future. The question is whether we just deal with it now."

After losing the 1978 and 1981 elections despite receiving the most votes, the Labour Government under David Lange set up the Royal Commission on the Electoral System to look into a better way of choosing our representatives in Parliament.

When the commission reported back in late 1986, it recommended ditching first-past-the-post (FPP) and adopting German-style Mixed-Member Proportional (MMP) representation with a 4 percent threshold.

A review in 2012 by the Electoral Commission reaffirmed experts' views the threshold should be dropped, as well as abolishing the coat-tailing rule - which allows parties which win an electorate seat to bring in more MPs, even if they don't meet the usual threshold.

In recent years the biggest beneficiary of this rule has been ACT - in 2008 the party got five MPs into Parliament with only 3.65 percent of the vote. In 2017 it got one MP, despite polling well below both the Opportunities Party and the Māori Party, which got none.

Mr Little says it was also "unfair" the Conservative Party missed out on getting into Parliament in 2014.

"The ACT Party is the only one-member party at the moment. They get their one seat, but their votes across the rest of the population mean they don't qualify for extra people. It's only if you get that extra 2, 3, 4 percent where you might feel like you're missing out."