New Zealand’s prime minister Christopher Luxon has defended his government’s plans to overhaul its electoral laws, despite warnings from his own attorney general the changes could breach human rights law and disenfranchise more than 100,000 voters.

The right-wing government last week announced its plan to shake up electoral laws it said were “outdated and unsustainable”, including closing voter enrolment 13 days before election day, reinstating a total ban on prisoner voting and prohibiting anyone from providing free food, drink or entertainment within 100 metres of a voting station.

Since 1993, voters have been allowed to enrol to vote during the two week advance voting period and, more recently, on election day, casting what is called a “special vote”.

Luxon told RNZ on Monday the late enrolments had led to weeks-long delays in counting votes.

“We want everyone to participate in our democracy … but we need to make sure that people are registered in advance of voting,” he said.

But in a report to parliament, the attorney general, Judith Collins, warned the proposal “appears to be inconsistent” with the Bill of Rights, including the right to vote and the right to freedom of expression.

Collins noted that during the 2023 general election, there were more than 200,000 special votes cast, including 97,000 people who registered for the first time during the voting period, and nearly 134,000 people who changed electoral districts during the voting period.

“This gives some indication of the number of people who may be affected, and the farther out the registration deadline from polling day, the greater the disenfranchising impact is likely to be,” Collins said.

Changing the enrolment deadline to one to seven days before polling day would “impose less onerous limits on the right to vote”, she said.

Special votes are more likely to come from younger people and areas with larger Māori, Asian and Pasifika communities, and these communities may be more affected by the proposed registration deadline, Collins said.

With respect to the blanket ban on prisoner voting, Collins said it would disenfranchise those who have a right to vote “and cannot be justified”.

Luxon said the attorney-general has a statutory obligation to examine whether legislation will contravene the Bill of Rights and the government would consider that advice.

Collins declined the Guardian’s request for further comment.

The proposed changes have drawn ire from opposition parties, who believe the government is weakening democracy.

“As a country we should be encouraging voter turnout and making changes to support that – not shutting them out,” said Duncan Webb, Labour’s justice spokesperson.

“This is an appalling change that will make it harder for a lot of people to exercise their democratic right.”