The Electoral Commission says it will write to nearly 29,000 people who voted on election day when they had not enrolled to vote.
They all had their votes disallowed, 95 percent of them because they were not enrolled in any electorate.
Chief Electoral Officer Robert Peden said the Commission would write to each of them encouraging them to enrol.
He said people can enrol up until the day before the election and allowing them to enrol on election day is considered from time to time.
"It's an option, it does have drawbacks in that if you've got a large number of people turning up to vote they have to enrol at the same time as they vote, it's just going to slow the process down for those who are already voting."
Social media rules also need consideration
The Commission also said rules governing social media during elections needed to be considered.
The law currently forbids the promotion of or attack against any candidate or party on voting day before the polls close at seven at night.
That includes any posts online, including on Facebook or Twitter.
Several sports stars ran afoul of that rule this year.
Mr Peden said Parliament should look at those requirements and how feasible it is to enforce them.
"We want to do whatever we can to make sure that New Zealanders stay on the right line of the rules.
"There isn't a high-level of awareness about what the requirements are, and that's something which needs to be looked at."
He said people also needed to consider the wider rules around electioneering on election day, given the increase in advance voting.