An error of judgement could cost Labour leader David Cunliffe thousands of dollars.
Mr Cunliffe now admits it was wrong to use a private trust to collect donations for his leadership campaign last year.
"I displayed an error of judgement. I take full responsibility," Mr Cunliffe says.
"Personally I think the rules around donations could be tightened. And that's something I will strongly support in the upcoming review," he adds.
Legally, he has done nothing wrong, the same rules do not apply to leadership battles, but it has opened him up to criticism.
"It's amazing that he's made this kind of error because this is the Labour Party that changed the rules around trusts. It's the Labour Party that's always claimed people should be transparent and upfront," says Prime Minister John Key.
Even Labour's potential coalition partner, the Green Party, is not impressed.
"I think it was disappointing that he used that anonymous trust. But I think it's good that he's come out now and fronted up," says Greens co-leader Russel Norman.
Act leader John Banks says Labour is being hypocritical.
"These are the same people that paraded in the house as paragons of virtue and railed against me day after day, week after week and month after month. They should look at themselves. These people are hypocrites," he says.
Today Mr Cunliffe revealed five donors made contributions over $500.
But only three would be named - Selwyn Pellet, Perry Keenan and Tony Gibbs. In total they gave $9,500. The other two donors refused to be named.
"In their case, the trust will be returning the donations to them. That amounts to $8,300," says Mr Cunliffe.
He has promised to pay the money back himself if necessary.
But damage within Labour's ranks may be more costly, with some telling ONE News privately that they think hopes of an election victory are gone.