The Electronic Frontier Foundation (EFF) is taking AT&T to court claiming that the US comms giant helped the US National Security Agency (NSA) to conduct illegal domestic spying operations.

The suit alleges that AT&T gave the NSA direct access to its databases of communications records, including detailed information about its customers' phone and email correspondence. 

"AT&T's customers reasonably expect that their communications are private and have long trusted AT&T to follow the law and protect that privacy. Unfortunately, AT&T has betrayed that trust," said EFF senior staff attorney Lee Tien.

"At the NSA's request, AT&T eviscerated the legal safeguards required by Congress and the courts with a keystroke."

The lawsuit also alleges that AT&T gave the government unfettered access to its 300 terabyte Daytona database of caller information. Daytona is one of the largest databases in the world. 

The EFF also alleges that, by opening its network and databases to wholesale surveillance by the NSA, AT&T violated the privacy of its customers and its customers' telephone and email correspondents, and has broken longstanding communications privacy laws.

The lawsuit further alleges that AT&T continues to assist the government in its covert surveillance of millions of Americans.

The EFF said that it is suing to stop this illegal conduct on behalf of a nationwide class of AT&T customers.