Human Rights Watch (HRW) has lodged a complaint against the UK Government Communications Headquarters (GCHQ) for intercepting, using, and retaining its communications.
HRW and three individuals filed the complaint with the Investigatory Powers Tribunal (IPT). It alleges that the organisation's rights were violated through unlawful surveillance, and in particular, sharing of the data with the US National Security Administration (NSA).
The case follows a finding by the tribunal that Britain had unlawfully retained communications of Amnesty International.
Human Rights Watch general counsel Dinah PoKempner said: "If GCHQ has been collecting Amnesty International's communications, it is nearly certain that ours have been intercepted as well.
"Mass-scale surveillance and data swapping without suspicion or independent oversight pose a grave threat to the lives, safety, and work of human rights defenders, researchers, journalists, lawyers, and their sources.
"We are bringing this case because confidentiality of communications is critical for those who work to protect human rights and expose abuses and war crimes."
In February this year, the IPT ruled that GCHQ had accessed data from the NSA prior to December 2014, which violates the right to privacy and free expression, but withheld the names of those whose communications were part of those unlawfully shared.
The tribunal, however, noted that sharing had been lawful since December 2014, due to public disclosures of minimal safeguards.
HRW aims to challenge the adequacy of those safeguards at the European Court of Human Rights.
'Five Eyes' countries, including Australia, Canada, New Zealand, as well as the US and UK freely share information, with the GCHQ able to access data from the NSA without a warrant.
More than 25,000 people are claimed to have expressed interest in filing claims of unlawful surveillance with the IPT.
HRW previously joined as plaintiff in cases against the US Government for surveillance of its communications in the course of mass surveillance programmes, including First Unitarian Church of Los Angeles v NSA, Wikimedia v NSA, and Human Rights Watch v DEA.
Image: An aerial photograph showing Britain's Government Communications Headquarters in Cheltenham. Photo: © 2010 Reuters.