CityFibre has applied to take the Advertising Standards Authority's to court over its decision to approve the continued use of the term "fibre" to describe services delivered over copper-based networks.
Last year the ASA found it was "not materially misleading" for ISPs to describe copper hybrid services as "fibre broadband".
But CityFibre claimed the ASA's research and logic "was fundamentally flawed" and that it "has not only permitted, but also encouraged Internet Service Providers (ISPs) to continue to mislead consumers".
The issue of fibre advertising has become more contentious as a number of alternative network providers intend to roll out fibre-to-the-home.
In November, Vodafone announced a deal with CityFibre to build a full-fibre network, intended to connect 5 million premises over the next eight years.
The majority of broadband services delivered over BT Openreach or Virgin's infrastructure are reliant on all-copper or part-copper-part-fibre networks. However, BT's Openreach has since unveiled plans to connect 3 million premises to full fibre by 2020.
CityFibre chief exec Greg Mesch said: "The ASA's short-sighted decision to allow yesterday's copper-based infrastructure to masquerade as the future-proof full fibre networks of tomorrow is a clear failure in its duty.
"It has failed to ensure honest and truthful broadband advertising, it has failed to enable consumers to make informed choices and it has failed to support a national infrastructure project critical to our success in a digital age."
He said that without "clear and transparent advertising" consumers will be misled into staying on inferior, copper-based broadband services. "The first step to righting this consumer wrong is for the ASA to reverse its decision, which perpetuates the 'fake fibre' lie."
An ASA spokesman said: "We acknowledge that CityFibre has applied for a judicial review of our November 2017 decision on the use of the term 'fibre' to describe part–fibre services. The full reasoning for our decision is available on our website. We will be responding to the application in due course."
Full-fibre penetration in Blighty seriously lags behind its European peers. The UK is estimated to have fibre penetration of between 2-3 per cent, compared to Latvia, which has 50.6 per cent household penetration.
Matthew Hare, chief executive of fibre broadband firm Gigaclear, said the firm supported CityFibre's challenge. "Without the knowledge of how full-fibre differentiates from part-fibre, consumers are being blinded to the fundamental capabilities of services on offer.
"With part-fibre, the consumer is wholly reliant on the quality of the copper or other technology that is connecting them to the fibre backbone." ®