Labour leader Jacinda Ardern has reiterated her position to retaliate if university fees for Kiwi expats in Australia go up - but says she won't remove the ability for Australians to access welfare in New Zealand.

"On benefits I hold a different view. We are still fighting for New Zealanders' rights in Australia. I think we should maintain the moral high ground that it is only right that if you pay taxes you have access to those benefits," Ardern told media in Pukekohe today.

"So we have maintained them in New Zealand while we continue to argue for them in Australia."

In last night's Newshub leaders debate, Ardern and Bill English were asked about the Australian Government eroding the rights of New Zealand expats living in Australia, and whether they would retaliate with similar measures.

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English said he would not but Ardern, for the first time, said she would, saying if Kiwis in Australia were locked out of tertiary education, she would lock Australians out here.

Today, Ardern said that would happen only if fees went up significantly for New Zealanders living in Australia.

Labour has pledged to eventually roll out three years of free post-school study or training, which will also cover Australians living here. However, if fees go up across the Tasman then Ardern said Australians here will be charged international student fees.

"There has been talk of New Zealanders being locked out of having the same access to tertiary education in Australia as Australian students," Ardern said.

"Our view is if those rights are removed we should likewise do the same for our subsidised education in New Zealand."

Previous Labour leader Andrew Little travelled to Canberra in November 2015 to lobby for improved rights for the estimated 250,000 to 350,000 Kiwis living in Australia on "non protected" visas - including little welfare safety nets, and no automatic path to permanent residency or citizenship.

Labour and National-led Governments have been lobbying for change since Kiwis' rights were greatly reduced in February 2001 by John Howard's Liberal Government.

Tensions have also grown after a change to Australian law led to the deportation of New Zealanders who had served jail time or failed "character tests". Many have been held in deportation centres while appealing the deportation.

The Oz Kiwi lobby group has been advocating for improved rights for New Zealanders living in Australia, particularly an easier path to citizenship.

Last night, the group tweeted its opposition to Ardern's retaliation threat, saying "denying rights to one group doesn't solve the issue for another group".

Ardern was not long leader of Labour when Australian Foreign Minister Julie Bishop said she would find it hard to trust a Labour Government.

Her extraordinary comments came after Labour MP Chris Hipkins asked citizenship questions following contact with an Australian Labor staffer and during questions over the citizenship of Australia's Deputy Prime Minister Barnaby Joyce.