When it comes to foreign influence, Australia is "by far the most pervasive influence" on New Zealand Opposition leader Bill English says.
In the security briefing to the incoming Prime Minister Jacinda Ardern, New Zealand's security agencies NZSIS and GCSB warned within the past year, foreign states have attemped to access Government and private sector information and "unduly influence expatriate communities."
Mr English said the most foreign influence comes from Australia.
He said when he was Finance Minister, there was "constant pressure" from Australian banks and insurance providers "over the way that New Zealand had different rules on our financial sector than they have in Australia".
"Over the years at different times there's been concerns about the influence of Russia, the US, China," he said.
"Of course, there's potentially pervasive influence from Australia, where they own our banks and insurance companies, and there's a lot of tension around that.
"The Australians would prefer we didn't regulate our own financial sector. They'd prefer to do that from Australia. That's much more immediate influence, I think, than the others."
New Zealand's "big four" Australian-owned banks are BNZ, ASB, ANZ and Westpac.
Raising the issue of Australian-owned banks could put Foreign Minister Winston Peters in a tricky spot.
As New Zealand First leader, Mr Peters said New Zealand was losing "a huge amount of money" because of the "big four".
"We're saying this level of foreign ownership, and in key institutions, is seriously bad for our economy because it disguises the state of the economy as it relates to benefits for New Zealanders," he told Interest.co.nz in July.
As part of New Zealand First's coalition agreement, the Government will investigate growing KiwiBank's capital base and capabilities "so that it is positioned to become the Government's Banker when that contract is next renewed" - an attempt to bolster a New Zealand-owned bank.