Nicky Hager's lawyer Felix Geiringer says the Dirty Politics author has the law on his side, as he fights to protect documents taken from his home from police scrutiny.
Police raided Mr Hager's home earlier this month, seizing documents and devices in a bid to identify the hacker known as Rawshark, a key source of Mr Hager's book.
Officers have not examined the seized devices, which are secured by the High Court.
Mr Hager is challenging the legitimacy of the search warrant.
Mr Geiringer said Rawhark was given an assurance of confidentiality, and the law said that when a journalist does that, the relevant information was privileged.
He said the legal challenge to the search also encompasses the fact police took away all Mr Hager's documents, which could compromise his other sources.
However, a Canterbury University law expert said current legislation may not protect information about sources stored in equipment seized from Mr Hager.
Canterbury University's Ursula Cheer said journalistic privilege may not apply to his work.
Ms Cheer said it was usually applied to commercial radio, television, and print journalists, and Mr Hager may be an exception since he writes books.
"That has to be for the purpose of breaking stories regularly in the news medium and writing a book may not actually fit that definition.
"I think it'd very generally accepted that his is a journalist, so it would be awful thing if that definition did not fit him in some way."
The Engineers, Printers, and Manufacturers Union said any attempt by police to access the sources of Mr Hager was an attack on media freedom.
EPMU senior industrial officer Paul Tolich said a ruling in favour of the police could set a dangerous precedent.
"It goes back to that age-old right of the journalist to remain silent about who his sources are, one of the pillars of the free press and one that needs to be defended, especially in this age where there is increasing surveillance."