Grant Robertson has defended the Prime Minister travelling separately to Nauru so that she can spend less time away from baby Neve.
Jacinda Ardern will attend this week's Pacific Islands Forum but will not go for the full length of time because Neve is too young to get all the vaccinations she would need to enter the island.
The RNZAF VIP jet will fly back from Nauru to pick her up on Wednesday at a cost of about $100,000 to the taxpayer.
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However the Finance Minister denied that her separate flight would cost taxpayers more, saying that the money for the flights had already been allocated.
"We allocate that money each year, so actually there is no additional money at all being spent there, it's simply making use of that 757."
He has defended her decision to attend the forum which newly-elected Australian Prime Minister Scott Morrison will not be going to, saying it's important New Zealand is represented at the highest level.
"I think if she didn't go to an important meeting like that we'd see a lot of criticism from people in the media as well, so she's probably damned if she did, damned if she didn't. She's taken the decision and I think it's the right one."
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He says New Zealand's Pacific relationships are its most important, and that having both the Prime Minister and Foreign Minister Winston Peters there is vital.
The Minister says certain allowances are simply part of having a leader who is a mother.
"We're just making sure a young mother can go up there and do her job, I think it's a great thing in 2018 that that's happening.
"Jacinda's doing her job as Prime Minister representing us and we should be proud of that."
He rejected The AM Show host Duncan Garner's accusation that the Government was being hypocritical by funding a separate flight but not offering Kiwi Abby Hartley financial help to be brought home from Bali in a medical coma.
"I have great sympathy for the Hartley family... but we're talking about two quite different things here. We're talking about the Prime Minister out there representing us, using a service that was already paid for, and making sure she's able to do her job in the circumstances that she's in at the moment.
"This is something that's quite appropriate for the Prime Minister to do, and I hope New Zealanders would want us represented with our Pacific Island neighbours in the way that we are."