Police are trying to use secret evidence to defend searching an activist's personal banking records without a warrant while hunting for the hacker Rawshark.
Activist and blogger Martyn Bradbury has provided the Herald documents showing the police are seeking a closed hearing of the Human Rights Tribunal to present evidence it does not want made public.
In an application to the tribunal from Crown Law, the lawyer acting for police said: "Police indicate at this stage that it will seek to invoke the "closed" hearing process in relation to information relevant to this claim."
Bradbury, who had been self-represented, said he was now talking to civil rights lawyers.
"I'm incredibly unhappy they are wanting part of this to be a secret trial with secret evidence."
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The step could mark the first time the tribunal accepted secret evidence in a closed hearing against the objections of the person who had brought the prosecution.
In a previous instance in which police presented secret evidence, it was with the consent of the person who felt maligned by an employment vetting process.
The police position is in contrast to the apology provided to journalist Nicky Hager after obtaining 10 months of his banking records without a warrant.
Hager, who wrote the book Dirty Politics based on information allegedly hacked by Rawshark, won from police the admission "Mr Hager had a reasonable expectation of privacy in relation to that information".
The tribunal hearing is the latest to emerge from a cosy arrangement which had developed between banks and police, which has seen banks handing over customer information wholesale to police without any legal basis for doing so.
The practice saw police exploit a section of the Privacy Act, which allows agencies holding people's information to provide it without legal order if doing so would help "avoid prejudice to the maintenance of the law".
Banks were meant to ensure police provided "enough information to justify the disclosure" so they could make a decision.
In practice, it was simply provided without cause and some banks used it as a red flag warning about customers and closed down credit opportunities.
Bradbury alleges this is what happened in his case, and the effect of being refused credit without understanding why contributed to mental unwellness that ultimately led to attempts to self-harm.
He has also maintained there is nothing which could possibly link him to Rawshark as he had nothing to do with the hacking.
Barrister Felix Geiringer, who acted for Hager in the Dirty Politics fallout, said it was a matter of law that procedures in hearings which were hidden from other parties were "extraordinary" and only to be used in "extremely limited circumstances, if ever".
"There is a serious question as to what the possible justification could be."
Geiringer said the case involving Hager meant there would also be "serious questions" as to whether any justification would survive proper scrutiny.
He said the difficulty with closed hearings was it deprived affected parties from applying such scrutiny to secret testimony.
The police concession in the Hager case included recognising the law had been clarified through a recent Supreme Court ruling.
"In light of that judgment, Police accept that they needed to obtain a production order in order to obtain Mr Hager's banking information," said police.
In Bradbury's case, the Privacy Commissioner John Edwards has already ruled police "were not justified" asking for the banking records.
"It is our view the request for your banking records, given their sensitivity, ought to have been placed before a judicial officer for decision on whether it met the grounds for a production order."
A spokesperson for police said no comment would be made because the case was before the tribunal.