Seven internet service providers from around the world have lodged a formal legal complaint against GCHQ, citing allegations that the government's intelligence agency used malware to illegally access their networks.
The claims are substantial, coming from seven ISP providers across six countries - the UK, Netherlands, US, South Korea, Germany and Zimbabwe. They follow a series of revelations about government snooping on private communications of citizens from former NSA IT contractor turned whistleblower Edward Snowden.
The attacks against networks, which have been outlined in German newspaper Der Spiegel, have been labelled by ISP providers as illegal and a matter that undermines the trust that customers of the internet providers rely upon.
The allegations, which are being filed to the investigatory powers tribunal (IPT) court in London, include claims that GCHQ and the NSA used a range of network exploits to intrude on the activities of network users.
It's also suggested that Belgium telecommunications firm Belgacom was a target of attacks by GCHQ which enabled government agents to gain access to its networks, while German internet exchanges were also allegedly targeted, allowing the British authorities to spy on their internet traffic.
"These widespread attacks on providers and collectives undermine the trust we all place on the internet and greatly endangers the world's most powerful tool for democracy and free expression," said Eric King, deputy director of Privacy International, a privacy campaign group.
"It completely cripples our confidence in the internet economy and threatens the rights of all those who use it. These unlawful activities run jointly by GCHQ and the NSA, must come to an end immediately," he added.
The claimants include British ISP provider GreenNet Ltd, which has called for an end to intrusive mass surveillance.
"Snowden's revelations have exposed GCHQ's view that independent operators like GreenNet are legitimate targets for internet surveillance, so we could be unknowingly used to collect data on our users," said GreenNet's Cedric Knight.
"Our long-established network of NGOs and charities, or simply individuals who value our independent and ethical standpoint, rely on us for a level of integrity they can't get from mainstream ISPs. Our entire modus operandi is threatened by this illegal and intrusive mass surveillance," he added.
All GCHQ has said on the matter is that all its work is carried out "in accordance with a strict legal and policy framework that ensures that our activities are authorised, necessary and proportionate."