Telecom and Vodafone are in a High Court scrap over an allegedly misleading ad campaign.
Telecom, the country's biggest phone company, is claiming aspects of Vodafone's new "SuperNet" advertising is misleading to consumers and a breach of the Fair Trading Act.
Telecom wants the campaign changed or pulled and has filed an injunction in the High Court.
The advertising describes Vodafone's infrastructure "as the best fixed-line network".
The Weekend Herald understands Telecom also takes issue with Vodafone calling its cable network in Wellington and Christchurch "ultra-fast broadband".