Police told Westpac it wasn't "doing something wrong" when it handed over Nicky Hager's banking data with no legal compulsion during an investigation into a hacker.
The comment is included in police emails sent after the disclosure of the intrusion into Hager's banking records and show detectives tried to maintain access to private financial information held by banks.
The relationship between banks and the police was fractured when the Weekend Herald revealed last year that officers hunting for Rawshark - the source who provided information for the book Dirty Politics - were handed Hager's transactions for a 10-month period.
As a result, Westpac announced publicly it would only provide banking information to police if a legal compulsion order was received. Without it, it would only confirm an individual was a customer.
Police had obtained financial details using a clause in the Privacy Act which allowed banks to provide the information if it believed police had provided evidence it was needed to help keep law and order.
Emails released under the Official Information Act show Detective Superintendent Paul Berry - the police's contact person with the banks - attempting to encourage banks to continue providing information after the Hager disclosure had become public.
He told Westpac after it insisted on a production order or search warrant that "a sudden change to a black and white rule as indicated ... only serves to indicate to an outside observer that the bank must have been doing something wrong [when they weren't], that's why they made the sudden change".
He warned: "It will also have unintended consequences which may result in further negative publicity for banks, e.g, where banks hold information that could have prevented harm but they would not release it to police despite police not being able to provide a PO [production order]".
Mr Berry said: "To make changes because of one case is disappointing."
A police spokesman said police were currently "revising" the request for information sent to banks.
"The new form will ... include more details about the police investigation so that banks can properly inform themselves before they can release limited information."
The Privacy Commissioner's transparency reporting study, from February, showed about 1000 requests citing the "maintenance of the law" exception in the Privacy Act over a three-month period last year.
A spokesman for the commissioner, John Edwards, said there had been a recommendation to police they review their request forms to make it clear companies receiving them were "under no obligation to comply".
He said banks and other companies involved in the trial had reported they took the requests "at face value" and believed they had to comply with the request because "they are from the police and it's about a crime".
The spokesman said ... the banks had "specifically asked for guidance" around the exception, which is Principle 11 of the act, "after what happened in the Hager case".
Westpac said yesterday: "We take our responsibility to protect customer information seriously." The bank would only disclose information about customer transactions "if we have received an appropriate order or warrant or the customer has consented to the disclosure".