The FBI is considering appealing against a New Zealand court ruling that would allow Kim Dotcom's legal team to view evidence gathered against him.
The United States is seeking to extradite the Megaupload founder to face charges of internet piracy, money laundering and fraud.
Mr Dotcom's lawyers had requested to see the evidence which was going to be used against their client.
But Crown lawyers, representing the US authorities, opposed this.
On Tuesday in Auckland District Court, Judge David Harvey ruled that Mr Dotcom's lawyers should have access to some material relating to the extradition hearing, which is set down for August.
Mr Dotcom's lawyers had sought disclosure of all documents relating to all charges.
Judge Harvey said the documents to be revealed should apply only to the proceedings in New Zealand.
Megaupload was indicted in a federal court in Alexandria, Virginia, on 19 January and the site was shut down. Mr Dotcom and his three co-accused were arrested in Auckland the following day.
Formal papers requesting their extradition were lodged in early March.