The coalition will introduce legislation on a four-year Parliamentary term, subject to a referendum, with all three parties supporting it to a select committee.

The legislation will have a caveat, designed by the ACT Party as part of its coalition deal, that the term would only extend to four years if there were greater checks and balances on the government of the day.

It would mean unless the make-up of select committees was made proportionate to non-Executive members of Parliament, the term would remain at three years.

Justice Minister Paul Goldsmith made the announcement on Thursday saying, "as stipulated in the National-Act coalition agreement, the Bill is modelled on the ACT Party's draft Constitution (Enabling a 4-Year Term) Amendment Bill."

"The main condition is that membership of certain select committees is calculated in a way that is proportionate to the non-Executive parliamentary party membership of the House.

"Given the constitutional significance of the term of Parliament, this change would be subject to the outcome of a binding referendum," he said.

National and New Zealand First's support is only guaranteed through to select committee, where changes could still be made, including a referendum at next year's election on a straight three or four year term.

"Both the National-Act and National-New Zealand First coalition agreements include supporting the Bill to select committee. At this stage, no decisions have been made on whether the Bill will proceed beyond this," Goldsmith said.

"It is possible a referendum could be held alongside the next General Election in 2026. However, any final decisions on timing for a referendum will depend on what comes out of the select committee process.

"Future decisions will also need to be made by the Government as to whether the bill proceeds as introduced, or whether it should be amended."

Goldsmith added that the government wanted to hear from New Zealanders what they think during the select committee process.