Several Labour MPs are refusing to endorse leader David Shearer just a day after the party's annual conference changed the rules to make a leadership challenge likely in February 2013.
Under the changes, party members and affiliated unions will get to vote in future leadership contests as well as MPs.
Mr Shearer will need to get more than 60% support from his MPs in February when the party's next leadership review occurs to prevent a challenge.
The rule change is seen as a victory for his likely challenger, senior MP David Cunliffe. Other MPs Sue Moroney, Louisa Wall and Moana Mackey have already refused to endorse Mr Shearer as leader.
Some MPs who support Mr Shearer believe he should put the leadership to the vote now to finally end speculation about the matter.
David Shearer became leader in December last year when he beat Mr Cunliffe in a vote among MPs only and on Saturday told reporters he is confident he will hold on to the job.
"We don't know what the vote was last year - nobody knows that. I am confident that I will have the numbers and the vote next year to ensure that I am the leader going into 2014. I can guarantee that."
On Sunday, he told party members at the conference they had to be unified if they wanted to win the support of the country.
In last-minute changes to his speech, Mr Shearer made reference to questions raised about his leadership after Saturday's vote to change the way the leader is elected.
He said Labour had to show New Zealanders that it was more focused on their ambitions than on any personal political ambitions.
Mr Shearer told the conference he was not the leader to indulge in some sense of celebrity, but to help improve people's lives.
After his speech Mr Shearer would not be drawn on any potential leadership challenge.
He refused to say whether a vote would be forced before the scheduled leadership review in February, but if there is one, he will be setting the timetable.
Cunliffe supportive - for now
David Cunliffe said on Sunday that he supports the leader for now, but continues his refusal to commit to endorsing Mr Shearer when required to in February.
"We just don't know what the situation's going to be in February. And as I've said before, that is a caucus matter and I'm not going to pre-empt the caucus."
Mr Cunliffe also dodged the question, when asked if he had set any leadership ambitions aside, after his unsuccessful bid in December.
But senior MP and former leader Phil Goff says Mr Cunliffe could end any speculation today.
"I think David Cunliffe just needs to come out and say of course he supports the leader.
"He's properly elected, he's been there 10 months, he's done a good job, he's narrowed the gap in the polls - why wouldn't you get behind and support your leader."
Mr Goff says he is solidly in support of David Shearer.
On Saturday, deputy leader Grant Robertson praised Mr Shearer's leadership and reminded delegates of the progress Labour had made since the 2011 election.
"The chance to put into action our values is in reach if we all focus on our common purpose. Under David Shearer's leadership, we have the plan, we have the policies and we have the people to make a better New Zealand built on compassion, hope and fairness."
Mr Robertson warned delegates that Labour should not fall into the trap of letting itself be split by divisions.