"Given the political elements to the case, I'm concerned that any government agency that answers to the Prime Minister will be seeking so broadly information from a journalist when that information comes from someone who has a political motivation involving the Prime Minister," he said.
Prime Minister John Key is the minister responsible for the GCSB. Mr Key's office said he was not briefed on Crown Law's request.
Under High Court rules, Crown Law could apply to a judge to have the documents released.
Crown prosecutor Aedeen Boadita-Cormican said in a letter to Fisher that if he was unwilling to provide the material her client reserved the right to apply for a court order.
Legal expert Ursula Cheer, from the University of Canterbury, said that if an order was made Crown Law would have to contend with the special privileges afforded to journalists. These privileges could extend to Fisher's research for his book.
Professor Cheer said courts were careful about compelling people, in particular reporters, to give up information.
"Although ... it is a privilege that can be displaced - it's not a right for journalists to say they want to protect their sources. The judges do their best to observe that, but they can overturn it if, for example, someone cannot get the evidence somewhere else," she said.
A judge was also likely to disallow any "fishing expeditions" for information, she said.
If Fisher had provided Mr Dotcom with transcripts, Mr Dotcom would have had to release them as part of the case's discovery process. But Fisher did not provide transcripts, so Crown Law had to ask him whether he was willing to give them up.
