Westpac breached investigative journalist Nicky Hager's privacy by giving police his personal information, the privacy commissioner has found.
In the lead-up to an unlawful 10-hour search of Hager's Wellington home in October 2014, police requested more than 10 months of his bank transactions without a warrant.
Banks are allowed to give out customer information, but only if they believe it's a necessary part of a police investigation.
But Hager's lawyer, Felix Geiringer, says police falsely told the bank Hager was being investigated for fraud and the bank asked for no further evidence before turning over the information.
In a newly released decision, Privacy Commissioner John Edwards upheld Hager's complaint.
"The effect of Westpac's submissions would appear to be that it believes that every customer has authorised the disclosure of all of their information from each of their accounts to police for whatever reason police give, without recourse to production orders or other authorities," he said.
"I simply cannot accept that is a well-founded belief."
Comment has been requested from Westpac.
In December, a court found a 10-hour search of Hager's Wellington home in October 2014 was illegal because police had not told the court they were conducting a "media search" when they applied for a warrant.
The search took place in the aftermath of the release of his book Dirty Politics, which was based on information taken from WhaleOil blogger Cameron Slater's emails and online communications.
The information was given to Hager by an anonymous hacker and the search was part of a police investigation to identify that person.
Hager sought a judicial review of the way police applied for a search warrant, the subsequent granting of the application, and the way the search was carried out.