The police are taking the investigative journalist Nicky Hager to court in a bid to access information he wants kept secret, Radio New Zealand reports.
Source material for his book, Dirty Politics, which alleges underhand activity by National Party politicians.
Hager's lawyer, Felix Geiringer, said the police seized items in the search of his client's home.
However, they were sealed with the High Court when Hager claimed they were privileged.
The police are now asking a High Court judge to let them review the documents.
In a separate legal bid, Hager's lawyers plan to challenge the search warrant used.