Vodafone operates in 29 countries all over the world. Reuters

In one of the biggest disclosures of government surveillance since Edward Snowden's revelations last June, the world’s second-largest telecommunications company, Vodafone (VOD.L), has revealed that several countries quietly wiretap its customers and listen in on their conversations.

On Friday, U.K.-based Vodafone released a report that discloses its forced compliance with laws that allow authorities in a handful of the 29 countries in which the company operates to directly access communications over its networks.

Vodafone’s Law Enforcement Disclosure Report is the most comprehensive review yet of the increasingly widespread use of phone and broadband networks to listen in on citizens.

While most intelligence agencies are required to file requests with Vodafone before being allowed to listen in on customers’ conversations, in six countries governments have “permanent” access to Vodafone’s infrastructure and are not required to file interception requests with Vodafone before snooping. These countries essentially have unlimited reign over Vodafone’s data.

Vodafone did not say which countries required obligatory access to its network, citing legal reasons for why they could not do so.

“Refusal to comply with a country’s laws is not an option,” the company said. "If we do not comply with a lawful demand for assistance, governments can remove our license to operate, preventing us from providing services to our customers.”

In most other countries, including the U.K., intelligence agencies must obtain a warrant to eavesdrop on phone calls or read text messages, emails and Web chats.

In some cases, wiretaps allowed agencies to listen to or record live conversations and even track the whereabouts of a customer.

"These are the nightmare scenarios that we were imagining," Gus Hosein, executive director of Privacy International, which has sued the British government over mass surveillance, told The Guardian. "I never thought the telcos [telecommunications companies] would be so complicit. It's a brave step by Vodafone 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."

Vodafone has 400 million customers across Europe, Africa and Asia. The company does not operate in the U.S. because it does not have an operating license there.

Of the EU countries in which Vodafone operates, Italy has made the most requests for customers’ data, the report showed.

Vodafone said it released the report to lay bare the “principles, policies and processes we follow when responding to demands from agencies and authorities” and to “disclose the aggregate number of demands we received over the last year in each of our countries of operation” unless otherwise prohibited.

Government surveillance has been a major controversy since National Security Agency whistle-blower Snowden revealed the extent of U.S. intelligence gathering last year and raised the alarm over privacy concerns.