UPDATE: Labour leader David Cunliffe is suggesting Prime Minister John Key had a hand in a smear campaign against him.
Mr Cunliffe has questioned how the PM knew about a letter Mr Cunliffe wrote for Donghua Liu two weeks ago.
The Labour leader says he wasn't told of it until half an hour before it was released.
"I think you should ask the government how come the Prime Minister had a copy of that letter two weeks earlier when the media put in an OIA on Monday," Mr Cunliffe said this afternoon.
EARLIER: Grant Robertson and David Parker appeared with David Cunliffe at a joint press conference in at Parliament at 1.45pm this afternoon, pledging loyalty.
Most pundits regard Mr Robertson and Mr Parker as the only credible candidates to try and tumble the Labour leader.
Mr Cunliffe said there was no question of a challenge.
Mr Robertson said, "I support the leader, that's why I'm here."
This morning, Mr Robertson and fellow senior Labour MPs Annette King, Jacinda Ardern, Clayton Cosgrove, Chris Hipkins and chief whip Sue Moroney reportedly met with Mr Cunliffe.
But if there was any attempt to to nudge the Labour leader into walking the plank, it appears to have fallen flat.
The meeting was to catch up on the events of the past 24 hours, Mr Robertson said.
He added that Mr Cunliffe had not asked him to rule out a challenge. He had not offered any assurance "because it was not necessary to have that as part of the conversation. It's not an issue. I assured him that I absolutely support him. I have no intention of challenging him before the election."
From tomorrow, Labour MPs enter a window where they can remove their leader by a simple majority vote (under the party's convoluted new leadership election system, caucus can otherwise be outvoted by party members and affiliated unions who supported Mr Cunliffe's election).
The conventional wisdom is that it's perilous to roll your leader this close to an election — as Labour discovered in 1990 when it traded Geoff Palmer for Mike Moore in a failed last-minute bid to regain ground.
However, the latest poll is so dire that even senior list MPs such as Ms Ardern and Andrew Little face losing their places in Parliament, a prospect that could potentially galvinise them into action.
But at this afternoon's standup press conference, Mr Cunliffe said he had the full support of caucus.
Mr Little — the media-savvy former EPMU boss once seen as a leadership contender — has kept a relatively low profile during his first term.
Today, asked if their would be an attempt to roll Mr Cunliffe, he replied, "I strongly doubt it. I've got my head down in work and haven't spoken to every colleague but I do not conceive of it being even a remote possibility."