Privacy International has appealed to the High Court to strike down a key part of the Investigatory Powers Bill that allows the government to issue blanket hacking warrants to GCHQ.
The so-called "thematic warrants" contained in the so-called Snooper's Charter allow the spy agency to hack into the computers and phones of people both inside and outside the UK.
Unlike normal warrants, they do not require a single target to be named and can instead be used to cover an entire class of unnamed property or persons, such as "all mobile phones in Nottingham" in the example given by the campaign group.
Privacy International initially raised a complaint about these general warrants in 2014, when it took its case to the Investigatory Powers Tribunal (IPT), which oversees agencies including GCHQ.
The campaign group had argued that such blanket warrants have no basis in UK law and also violate Articles 8 and 10 of the European Convention on Human Rights (ECHR) - the rights to privacy and freedon of speech. However, the IPT ruled in favour of the government in February this year.
Consequently, the organisation has taken its case to the High Court, seeking to overturn the IPT's ruling. As well as its claims that thematic warrants violate the ECHR, the group is also claiming that it undermines 250 years of English common law, which it claimed "has long rejected general warrants".
"The IPT's decision grants the government carte blanche to hack hundreds or thousands of people's computers and phones with a single warrant," said Privacy International's legal officer, Scarlet Kim. "General warrants permit GCHQ to target an entire class of persons or property without proving to a judge that each person affected is suspected of a crime or a threat to national security."
"By sanctioning this power, the IPT has upended 250 years of common law that makes clear such warrants are unlawful. Combined with the power to hack, these warrants represent an extraordinary expansion of state surveillance capabilities with alarming consequences for the security of our devices and the internet," Kim added.
Saying that these thematic warrants are a keystone of the Snooper's Charter, Privacy International claimed the entire bill could be called into question should it win its case in the High Court.
The group is not the only body to express concern over the inclusion of the warrants in the IP Bill. In February, the Intelligence and Security Committee (ISC) recommended "substantive amendments" to the wording of the bill, adding that it was unconvinced by some of the legal frameworks for its implementation, including various hacking warrants.
The lawfulness of bulk data collection under DRIPA - the emergency stop-gap regulation the government hopes will be replaced by the Investigatory Powers Bill - has also been challenged by MPs Tom Watson and David Davis, with the case currently progressing through the European Court of Justice (ECJ).
If DRIPA is found to break the rights to private and family life as defined in the Charter of Fundamental Rights of the European Union, it could scupper many of the plans laid out in the Snooper's Charter as well.
