The Labour Party faces the prospect of another leadership contest early next year after its annual conference agreed to change the rules for electing its leader.
The party is holding its annual conference in Auckland at the weekend which organisers say has the largest attendance since the late 1980s. More than 600 delegates are present.
In order to avoid a challenge in February, David Shearer will need the support of at least 60% of the caucus.
Radio New Zealand's parliamentary chief reporter at the conference says there were passionate speeches during the rule change debate, with MPs mounting arguments for both sides.
The new rule will apply to the regular, three yearly review of the leadership which follows general elections.
That review will happen in February - last year's was postponed because of the leadership contest that was won by Mr Shearer.
At any other time a majority caucus vote would be needed to trigger a challenge.
In either case, the leadership would then be put to a wider vote; party members would get 40% of that vote, MPs 40%, and affiliated groups 20%.
Last year's unsuccessful leadership candidate David Cunliffe is refusing to rule out a challenge, if there is a contest next year.
Mr Cunliffe says he disagrees with some caucus colleagues who argued a 40% trigger would have a destabilising effect on the caucus.
Mr Shearer says his position as leader is made no more precarious by the rule change, and Mr Cunliffe expressed his loyalty to him as recently as last week.
He says the rule changes to how the leader is elected make the party more modern, democratic and transparent and give members a greater say in the way the party is run.
Mr Shearer says the rule changes bring Labour into the 21st century.
Challenge to convince voters Labour represents 'hope and change'
Labour Party delegates have been told the challenge now is for the party to convince voters it represents hope and change - and that it is fit to lead the country.
Party president Moira Coatsworth used the recent re-election of Barack Obama in the United States as an example of a progressive government that can capture the popular vote.
Ms Coatsworth told party members on Saturday that the turnout in the 2011 general election contributed to Labour's defeat.
"The truth is, many people no longer share that hope and faith in political change. Last year's election turnout was New Zealand's lowest in a very long time. In Labour, about two-thirds of our vote loss was from people who didn't think it was worth voting at all."