A statement of claim by Vodafone against Telecom's new 3G mobile network reveals a big jump in disconnections by Vodafone clients.
Telecom plans to launch its XT network on 13 May, but Vodafone wants an injunction to stop the launch, claiming the network is interfering with its own cellphone signals.
The statement of claim was lodged on Monday. Both parties are to argue the case in the High Court in Auckland on Wednesday.
Vodafone says Telecom's interference seriously obstructs and interrupts communications on its network, causing reduced coverage, broken speech, and dropped calls.
As a result, it says the number of customers cancelling their connections has increased by 154%.
Vodafone says it started monitoring the problem in January and Telecom acknowledged the interference in April.
Telecom says it will vigorously defend itself in court.