CityFibre is taking the UK's advertising watchdog to court over its decision to allow copper-based broadband to be advertised as "fibre".
Last year, the Advertising Standards Authority (ASA) ruled that using the term "fibre broadband" in adverts for part-fibre services is not "materially misleading".
The decision was taken following a review which found that while consumers did notice fibre claims in ads, consumers regarded it as a "shorthand buzzword to describe modern, fast broadband".
Furthermore, the ASA said the word "fibre" is not a priority identified by consumers when choosing a broadband package.
However, CityFibre is maintaining that consumers are being "actively misled" if adverts for copper-based products are promoted as "fibre".
This, it said, is because the presence of copper in a part-fibre network results in slower download and upload speeds, whereas full-fibre services are capable of achieving Gigabit speeds (1,000Mbps) and are far more reliable.
The organisation has therefore filed for a judicial review of the ASA's ruling, on the grounds that the research and logic that led to the decision was "fundamentally flawed".
CityFibre is also arguing that the ASA's "lax advertising rules" both permit and encourage broadband providers to continue misleading consumers.
Indeed, it pointed out that unless the rules are changed, the growing number of consumers with access to full-fibre risk being unable to make informed purchasing decisions between "these two radically different technologies".
Greg Mesch, Chief Executive of CityFibre, commented: "You could hardly expect an automotive manufacturer to get away with advertising an 'electric car' when the most electric part of the car was its windows.
"The time has come to do away with 'fake fibre'."
Mr Mesch described the ASA's ruling as "short-sighted" and "a clear failure in its duty", as it has not ensured honest and truthful broadband advertising.
Furthermore, he said the decision means the watchdog has missed a chance to support a national infrastructure project critical to the UK's success in a digital age.
Mr Mesch warned that without clear and transparent advertising to guide people's purchasing decisions, millions will be "conned 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," he added.