The Chief High Court Judge has reserved a decision that will determine whether Kim Dotcom's legal team will get to see copies of evidence against their client.
Mr Dotcom was arrested in January when 70 police raided his mansion near Auckland during an investigation into the Megaupload website he co-founded.
The FBI is seeking to extradite the internet entrepreneur to the United States to face copyright, money laundering and fraud charges.
In May, a District Court judge ruled the authority should hand over copies of evidence to Mr Dotcom's lawyers so they could prepare for the extradition case in August.
The Crown, acting on behalf of the FBI, appealed against that ruling.
At the High Court in Auckland on Wednesday, Mr Dotcom's lawyer Paul Davison said his client needs the information to be able to defend himself properly.
Crown lawyers say they have already provided a summary of evidence, and that is all that is required.
Though Justice Winkelmann reserved her decision, a ruling is expected soon.