A former Conservative Party board member is calling a court ruling, that stopped a telecommunications company from disclosing his private emails, a landmark decision.

John Stringer is being sued for defamation by former Conservative Party leader Colin Craig after a public stoush between the two during the Dirty Politics saga.

Mr Craig brought Vodafone New Zealand into the discovery part of the case, in a bid to get hold of emails sent and received by Mr Stringer between November 2014 and February 2016.

His attempt was stopped short by a High Court judge late last month.

Mr Stringer said it would have been a huge breach of his privacy.

"That's why I think it's been dismissed. It contravened my rights under the Privacy Act."

Mr Stringer has compared the ruling to the recent landmark privacy case in the US.

"The FBI were requiring Apple to disclose confidentiality and encryption keys to its iPhone network so that they could have access to private correspondence."

Colin Craig has to pay Vodafone's legal fees for being dragged into the case.

Mr Craig didn't want to comment, saying it would be premature to comment on a particular ruling, seeing as the discovery process in the defamation case is ongoing.