The Kim Dotcom case threatens to pull New Zealand's most secretive spy agency into court in a bid which could probe intelligence links with the United States.
Mr Dotcom's lawyers have asked the High Court at Auckland to make the Government Communications Security Bureau a co-defendant in its legal challenge and order it to produce information relating to its illegal spying operation against the internet mogul.
The agency, which specialises in electronic surveillance, was called into the FBI operation against Mr Dotcom a year ago by the police Organised and Financial Crime Agency of New Zealand.
The spying, which took place over a month, turned out to be illegal, after the GCSB failed to check whether Mr Dotcom was a New Zealand resident. He was - meaning the bureau broke the law which bans it from spying on New Zealanders.
The admission by the GCSB made the surveillance before the January raid on Mr Dotcom's mansion in Coatesville illegal.
The police search warrant has also been ruled to be invalid, making the search and seizure illegal.
Mr Dotcom asked the court yesterday to join the GCSB to the case.
The Dotcom camp has suspicions about the involvement of the GCSB.
The agency is involved in the "Five Eyes" Echelon network which exchanges information among the US, Britain, Canada, Australia and here.
Chief High Court Judge Helen Winkelmann is expected to issue a decision next week.