CityFibre has been given permission by the High Court to proceed with its judicial review of the Advertising Standards Authority's (ASA) broadband advertising rules.
Last year, the 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 that 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 has maintained 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.
CityFibre also argued that the ASA's "lax advertising rules" both permit and encourage broadband providers to continue misleading consumers.
The organisation 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".
The High Court has given CityFibre the green light to proceed, which means the ASA has 35 days to prepare a counter argument, before the judicial review goes to court later this summer.
Greg Mesch, Chief Executive of CityFibre, commented: "The High Court is seeing sense where the ASA failed to: this is the right decision for consumers and our economy.
"CityFibre challenged the ASA's decision because consumers must not be misled into thinking they can get full-fibre benefits on a copper broadband network. They can't - copper is dead."
Mr Mesch went on to insist that the UK's advertising rules need to be sorted out "once and for all", while the government and industry must get behind the nationwide broadband targets set by the Chancellor.
Last month, Philip Hammond said he wants to see full-fibre broadband delivered to 15 million homes and businesses by 2025.
"Companies are investing billions because of the transformative connectivity full-fibre brings," Mr Mesch added.
"The Court has a one-off chance to step in and make a difference for consumers before the mis-selling of broadband becomes the next PPI-style scandal."