Caucus votes are worth more than other votes cast, with 34 MPs making up 40 per cent of the vote but the support of 17 MPs would give Mr Robertson a base of about 20 per cent of the total vote before membership and union votes are added.
Three unions have indicated not just Mr Cunliffe as No1, but are indicating Shane Jones as second preference and Mr Robertson as third. The two biggest affiliated unions, the Engineering, Printing and Manufacturing Union and the Service and Food Workers Union, have decided to make no recommendation.
The third biggest, the Meat Workers Union, with almost 4 per cent of the total vote, favours Mr Cunliffe first, Mr Jones second and Mr Robertson third.
National secretary Graham Cooke said that wasn't an edict but the consensus result after voting delegates had consulted their work sites.
He did not foresee any major problem if Mr Robertson ended up winning despite the apparent support for Mr Cunliffe. "If Cunliffe wins or Grant Robertson or Shane Jones I think the membership, the party and the hierarchy of the Labour caucus will be absolutely unified. I am very confident of that. We don't see any problems at all. One just needs to look at Australia to see what happens if you are dysfunctional."
The Dairy Workers Union has not declared its recommendation but it is understood to be ranking Cunliffe 1, Jones 2 and Robertson 3.
There are just two more hustings meetings with the three candidates appearing: tonight in Blackball on the West Coast, and tomorrow in Christchurch. Voting closes at midday next Sunday and the caucus will not know the result of the membership and union votes before they vote.
General secretary Tim Barnett said final results of the three sections - caucus, membership and affiliates - will be made public, as will earlier rounds if one candidate does not win a majority on the first vote and preferences are used.
Meanwhile, Mr Jones rejected a claim by Mr Cunliffe on One News last night that Mr Jones had made it clear to him in private and public he wanted his second preferences to go to Mr Cunliffe.
How the Unions' votes work
Six affiliated unions will cast votes that will comprise 20 per cent of the final vote, when combined.
The two biggest unions have not made any recommendation.
The four smaller unions favour Cunliffe.
Voting is secret and is conducted by the party.
Voting closes midday Sunday.
Engineering Printing and Manufacturing union
34.16 per cent of affiliate vote - 6.83 per cent of total vote
About 70 voting delegates
No recommendation to voting delegates
Service and Food Workers' Union
22.47 per cent of affiliate vote - 4.49 per cent of total vote
All members eligible to vote
No recommendation to voting members
Meat Workers' Union
About 45 voting delegates
19.8 per cent of affiliate vote - 3.96 per cent of total vote
Cunliffe 1, Jones 2, Robertson 3
Rail and Maritime Transport Union
6.21 per cent of affiliate votes - 1.24 per cent of total vote
26 voting delegates
Cunliffe 1, Jones 2, Robertson 3
Dairy Workers' Union
13.87 per cent of affiliate vote - 2.77 per cent of total vote
53 voting delegates
Cunliffe 1, Jones 2, Robertson 3
Maritime Union
3.49 per cent of affiliate vote - 0.69 per cent of total vote
18 voting delegates
Cunliffe No 1.
