Police say new rules key cog in crackdown on financial crime but change ignites fears of privacy erosion.
Banks will be forced to provide police with customer details on all cash transactions over $10,000 in a fresh crackdown on money laundering and the potential financing of terrorism.
Under new rules to be introduced from November, banks will give police sensitive information including names, locations and even phone numbers.
Police say it is a crucial step in gathering intelligence - but it has prompted fears of more erosion of privacy.
And banks say they can't rule out passing on the cost to customers in fee hikes.
New Zealand Council for Civil Liberties spokesman Thomas Beagle told the Weekend Herald police seemed to be gathering data without reason to suspect a crime.
"It's particularly worrying, police will be collecting all this information without the need for a warrant," he said.