The European Court of Human Rights has also asked the government to explain how GCHQ’s practices and oversight comply with the right to privacy.
Three has now joined Vodafone, O2 and Everything Everywhere in calling for more information on the system.
Three told Channel 4 News: “We take our customers’ privacy seriously. We are seeking clarity from the authorities following the reports of ‘Dishfire’ activity.”
Vodafone said it was “shocked and surprised” by the extent of the spying and would contact the government to challenge them over GCHQ’s use of Dishfire.
In a separate development, a group of British privacy campaigners have been told that their complaint to the European Court of Human Rights over GCHQ’s use of surveillance programmes has been made a “priority case”.
English PEN, Big Brother Watch and the Open Rights Group complained to the court that the bulk collection and analysis of data breached article eight of the European Convention on Human Rights.
Jo Glanville, of English PEN, said: “The European Court of Human Rights has made the action a priority. This only ever happens in a minority of cases and is a measure of the significant international concern about the UK’s unchecked surveillance.”
The government has been given until 2 May to respond. GCHQ told Channel 4 News when the revelations about Dishfire first emerged: “All of GCHQ’s work is carried out in accordance with the strict legal and policy framework which ensures that our activities are authorised, necessary and proportionate and that there is rigorous oversight.”