Telecommunications giant Vodafone today admitted the existence of secret wires that allow government agencies to listen in to conversations on its networks.
The company said the tapping is widely used in some of the 29 countries in which it operates.
Revealing its cooperation with state agencies, Vodafone said in a 20-page report entitled "Law Enforcement Disclosure" that direct wires are connected to its network, allowing live conversations to be listened to and recorded.
The wires also allow agencies to verify the location of a user.
Vodafone admitted that as a global business it faced "constant tension" while enforcing the laws of different countries and the "expectations" of governments.
"Refusal to comply with a country's laws is not an option," it said.
Vodafone said that in about six countries where it operates, phone tapping is required by law, although it did not identify the countries.
Vodafone said it was publishing the information as its contribution to the debate on government surveillance systems.
"The need for governments to balance their duty to protect the state and its citizens against their duty to protect individual privacy is now the focus of a significant global public debate," it said.
Privacy campaigners said Vodafone's disclosure confirmed their worst fears.
Gus Hosein, executive director of Privacy International, said: "These are the nightmare scenarios that we were imagining.
He told the Guardian newspaper: "I never thought the telcos (telecommunications companies) would be so complicit.
"It's a brave step by Vodafone (to admit it) and hopefully the other telcos will become more brave with disclosure, but what we need is for them to be braver about fighting back against the illegal requests and the laws themselves.
