The CTU itself is not affiliated to Labour - but many of the unions it represents certainly are and Cunliffe managed to secure almost three-quarters of the union vote in the leadership contest, helping make up the shortfall in the caucus vote in which he secured just one-third of the support. That meant he was elected leader without needing to go to second preferences.
The CTU conference was a wise choice for his first big speech. The sudden eruption of pro-union promises from Cunliffe during the leadership campaign had prompted scepticism in some that he did not necessarily believe what he was saying.
But audiences suspend scepticism when they hear what they want to hear, and what they heard from Cunliffe was first of all his prediction that Labour will win in 2014, followed by promises to bring an end to the "attacks on workers", to lift the minimum wage immediately, scrap youth rates, introduce a living wage, ensure pay equity, increase paid parental leave, and to force employers to see workers as "investments" rather than simply a cost to bear. He promised families would be able to pay their bills.
Only occasionally during his speech did he add his caveat of "as the country can afford". Even then, it was said in the same manner as the hurried voice at the end of advertisements that adds "special conditions apply". Details, schmetails.
Cunliffe went on to ask the unions for more support - in particular their help to get people out of their houses and to the polling booths at an election he described as being a turning point in the country's history. "Together, we will form the next government," he told them.
He also got in an implicit dig at his forebears in the role, promising under him, Labour would be "red, not a pale blue one".
There was a token effort to stop it slumping into the ideological category, when he said he would consider extending National's bonding scheme for professions such as doctors and teachers to include nurses, in return for writing off student loans. "Good ideas are good ideas wherever they come from."
It wasn't until afterwards when he was speaking to media that more emphasis was put on that big "but" of fiscal conditions.
It is here that the gift for National was presented. For in acknowledging it was the strong union support that helped ensure he got over the line, Cunliffe did not hold back from sending them the parallel message that he now owed them. National is sitting on its return to surplus like the goose over the golden egg, with maternal instincts on overdrive. It will grab at any opportunity to paint Labour as a nest-raiding ferret endangering that fragile recovery. And if Cunliffe can be painted as being beholden to the unions, all the better.
Nonetheless, the list of promises were music to the unions' ears. Speaking afterwards, both Kelly and the PSA's national secretary, Richard Wagstaff, were full of praise. "Wow," Kelly said. "That was fantastic." Wagstaff went further, saying that the things Cunliffe had said "are so dear to us and we are hungry for it".
And that was music to Cunliffe's ears. He'd just left a much trickier audience - his own caucus - after his first caucus retreat in Dunedin, where they indulged in team bonding by collecting cockles.
Cunliffe dismissed speculation he had sought individual pledges of loyalty from the caucus members, and threatened retribution on those from whom it was not forthcoming.
However, he chose his words carefully. Rather than say that he personally had the unanimous support of caucus, he said that there was unanimous support for the goal of becoming the government next year.
However hard National might try to paint the relationship between Cunliffe and the unions as one of unholy indebtedness, the upside of it for him is that a strong union mandate also gives Cunliffe power over that taciturn mob of his caucus.
So his speech to the unions was a signal to his caucus colleagues that, should they do anything to disrupt that goal of the government benches by undermining him, it would not only be him they had to answer to.
As for the likelihood those policies will be put into action, fiscal conditions may well apply in the end. But that can wait. Cunliffe has already shown he has learned one truism attributed to 18th century cook Hannah Glasse. First catch your hare.