It is thought Mr Shearer wants it to be declared, though that will be a decision of the caucus.
An anti-Shearer vote of between two and five MPs would not be surprising, being the residual camp of loyalists to New Lynn MP David Cunliffe, the party's former finance spokesman.
Mr Cunliffe was demoted for apparent disloyalty to Mr Shearer in the wake of the party conference at Ellerslie Racecourse in November.
He has said he won't be challenging Mr Shearer at today's vote, but he has not responded to questions about how he will be voting.
Under constitutional changes passed at the conference, the caucus, party membership and union affiliates would decided the leadership with a respective 40/40/20 split.
The constitution says the leadership has to be put to the vote by the caucus in the February preceding an election year. It has been common practice by the caucus to hold such a vote but that has been by dint of caucus rules, not a constitutional requirement.
After dealing to Mr Cunliffe last year, Mr Shearer has begun the year controversially with a state of the nation speech in Wainuiomata about the party's housing policy of building 100,000 affordable homes over 10 years.
National MPs teased him for using an autocue.
And media trainer Brian Edwards accused him of trying to be something he isn't in appearing to talk and act toughly.
"Shearer is a reasonable man, a conciliator by nature," Dr Edwards wrote on his blog last week.
"He has to stop trying so hard to be something he isn't. He can't carry it off and we will see through it. He is a poor actor."
But Mr Mallard, in his thank-you speech, likened Mr Shearer's speech to the first he heard from Mr Kirk on the steps of the Wellington City Library in 1972, the year of his landslide win.
Mr Mallard told the Herald that Mr Kirk had referred to the state housing programme of the then National Government as creating "little boxes to send the workers home to at night".
It was at the time of massive lower-quality state house building such as in Porirua and South Auckland, Mr Mallard said.
Mr Kirk injected a feeling of hope, which Mr Shearer also did.
"There is something there about having something to hope for, something to dream about. Shearer, possibly because he has spent so much time overseas, sees that as important for New Zealand."
Mr Mallard said there were other similarities too. "They are both real Kiwis but both are a bit diffident."
Other politicians of the day such as Sir Robert Muldoon and Bob Tizard were much more in your face, "whereas Kirk and Shearer would be more like the people down at the footy club".
