Six provisions of the Electoral Act 1993 are entrenched, which means that they can only be changed by a vote of more than 75% of the House of Representatives or more than 50% of voters in a referendum. One of the entrenched provisions relates to the Representation Commission, a committee which determines electoral boundaries.

A major review of the rules governing electoral redistributions occurred before the 1977 general election. At the same time the legal definition of 'Māori' was changed from one based on ethnicity to one based on cultural identity. Changes to electoral law allowed people to choose whether to go on the general or Māori electoral roll. Many people did not fill out the electoral re-registration card which accompanied census forms. For Māori this had a major effect – Māori who did not fill out the card were added to the general electorate. This, combined with northwards population drift, resulted in the creation of five new general electorates in the northern half of the North Island.