"If a trader is prepared to say it is "probably the fastest", this will suggest to many consumers that they have done their research and are comfortable they are performing at that level. In fact, Stuff Fibre had not verified its claim."
"Traders need to remember a claim is unsubstantiated if they do not have reasonable grounds to make the claim at the time they make it - irrespective of whether the claim is false or misleading."
Stuff Fibre managing director Sam Morse said it accepted the commission's decision.
The company had intended to highlight that it only sold ultrafast broadband, which it believed was the fastest and most reliable internet technology in New Zealand.
"The commission is very agitated about the telco industry and the telco sector and they are being very diligent, and we comply and we accept their decision," Morse said.
In September, heat pump supplier Fujitsu General New Zealand Limited was the first company convicted under the unsubstantiated representations provision of the Fair Trading Act and was fined $310,000.