He said the first thing he had said in his opening remarks at the party was that the Maori Party had made it clear it might work with Labour in the future.
The Maori Party has been criticised over the dinner because it involved Mr Key despite its claims to be able to work with either Labour or National. It has also been criticised because of the price tag and location of the dinner given its advocacy for low income Maori.
Labour's Shane Jones was derisive about it, likening it to "the dog returning to eat its own vomit." He said it was reminder that the Maori Party was tied to National.
"Without a doubt, it's the Prime Minister trying to shore up his position with the Maori Party. The reason you go to the Northern Club is it attracts people who have wealth. And the Maori Party need wealthy friends because they don't have any more marae friends."
He said the Maori Party was also guilty of double standards for criticising Hone Harawira for cuddling up to Kim Dotcom. "It's just a flasher version of having a choice of tea. In this case, it was an expensive hangi at the Northern Club."
Mr Key denied the dinner was similar to the 'cup of tea' deals with Act, which were a public signal for Epsom candidates to vote for Act's candidate in Epsom. He said those were intended to send a public message out, whereas fundraisers were not generally public.
He said every political party held fundraising dinners and it was not unusual to help out support partners.
"Unless we are going to move completely to state funded elections, political parties are going to raise money. It's no different to what Helen Clark did and probably many other Prime Ministers and leaders before me."
However, Mr Key said it was "a step too far"to interpret an upcoming fundraiser for the Act Party as a sign Epsom voters should support Act candidate David Seymour this time round.
He said National had made it clear that Act was a party it could work with after the election, but was yet to make a decision on whether to continue with a deal over the Epsom seat. Act's Epsom candidate David Seymour tweeted that he was very pleased Mr Key would be guest of honour at the campaign fundraiser.
"Everyday I campaign in Epsom to help keep John Key as PM."