Australian banks face having their wings clipped in New Zealand's $NZ210 billion mortgage market, as the country tries to quell a risky housing boom by further restricting bank lending.
The move to toughen credit rules across the Tasman comes as some local analysts suggest the Australian Prudential Regulation Authority (APRA) may require more tightening of bank lending to domestic property investors.
Economists from HSBC and AMP Capital say APRA should step up its supervision of domestic banks to the prevent risk building up in Australia's housing market - though others believe there is not enough evidence that debt-fuelled house price gains are back. 
The Reserve Bank of New Zealand last week signalled it would tighten restrictions on mortgage lending, which are already in place through limits on low-deposit lending in some areas. Rapid house price growth in Auckland had triggered "financial stability concerns", it warned.
The changes could slow New Zealand loan growth for the Commonwealth Bank, Westpac, National Australia Bank and ANZ Bank, which dominate the country's mortgage market, holding about $NZ180 billion in mortgages between them.
The tougher rules are likely to include further caps on lower-deposit lending, in addition to existing curbs on lending to investors who have deposits of less than 30 per cent in Auckland, where prices are still growing at double digit rates.
Another change being looked at is limiting how much a customer can borrow relative to their income.
Sean Keane of Triple T consulting said RBNZ governor Graeme Wheeler appeared to be moving "aggressively" by introducing the changes later this year
For the banks, such "macroprudential" changes are likely to limit growth potential, but also lower the level of risk in their New Zealand loan books. The changes could also lower margins, as higher-risk loans often have higher interest rates.
Housing is also a political issue across the Tasman, with the Labour Opposition saying price growth in Auckland was "out of control," and Westpac and ANZ last week both pulling the plug on lending to foreign buyers, similarly to recent moves in Australia.
However, there are significant differences between the two countries' housing markets.
New Zealand has not experienced the boom in apartment building seen in Australia, and migration into the country is at a record high.
"Australia caught up much more quickly and that in part because of the huge boom in apartment building," Mr Keane said.
Even so, some local analysts believe APRA will need to apply more pressure to the domestic banks, after strong growth in prices in   May and signs banks are competing more aggressively for investors.
At the moment, APRA has capped investor loan growth at 10 per cent a year. 
HSBC chief economist Paul Bloxham said there appeared a revival in Australian house prices, though it was not clear whether property investors were taking on more debt, which would add to risks. Figures last week showed new lending to investors dropped 5 per cent in   April, which could be a sign of tougher lending rules starting to bite.
"I think we may well see the prudential authority needs to turn up the dial to counter some of this revival of exuberance in the housing market."
AMP Capital chief economist Shane Oliver said APRA's 10 per cent cap appeared "quite excessive in the scheme of things".
Citi's Paul Brennan said he expected APRA would see to "lean against" any investor-driven boom in house prices, though this may be through tougher rules on bank lending, rather than changing the 10 per cent cap.