Civil liberties groups have protested over the issue
The US House of Representatives has passed a bill on anti-terrorism wiretaps that protects telecommunications companies from legal action.
This follows a long-running debate about the rights and wrongs of government eavesdropping and immunity for phone companies who help authorities do the eavesdropping.
What is this issue about?
After the 9/11 attacks, the US government started to monitor e-mails and phone calls in which one participant was abroad. It did so without going to a special court to ask for a warrant, arguing that there was no time. Phone companies agreed to provide the information but were subsequently sued for breach of privacy. Taps on communications wholly within the US still need a warrant.
A temporary law, the Protect America Act, was passed last year to allow for taps without warrants but it expired in February. President George W Bush's subsequent attempt to replace the temporary law triggered a fierce battle with the US House of Representatives.
What was Mr Bush's argument?
He said it would be dangerous if the Protect America Act was not renewed, but that any new legislation also needed to protect the telecom companies; otherwise they would be reluctant to co-operate for fear of being sued.
The Senate, he said, had passed a "good bill" and the House should do the same.
Why did the House of Representatives resist?
The House did not want to give the administration or the telecom companies a blank cheque. It argued instead that a court should decide in any legal case whether national security justified the companies giving their co-operation without a warrant.
The Senate agreed to give the companies protection.
How was the disagreement resolved?
The two sides reached a compromise in June 2008, whereby telephone companies would not be automatically immune, but courts would be obliged to dismiss a suit against a firm if it were able to produce written certification that the White House asked it to participate in the programme and assured the firm it was legal.
When did the issue of warrant-less eavesdropping first come to light?
In December 2005, the New York Times published an expose of the wiretap programme, triggering protests against the government from civil liberties organisations.
In January 2007, the administration reacted to the revelations by giving an assurance that it would in future seek warrants from the special court set up under the 1978 Foreign Intelligence Surveillance Act. However the court was swamped with warrant requests. In addition, it is believed that the court later ruled in secret that tapping without warrants was illegal. So the administration decided to seek a new law allowing it greater freedom. The Protect America Act passed into law in August 2007.
What did the temporary new law allow?
The Act allowed the US authorities to tap into phone calls and e-mails to or from the United States, as long as the target was abroad. The wiretapping used the switching centres in the United States that link phone calls and the internet worldwide.
The authorities want quick access to these communications, arguing that the old procedure of seeking a warrant from a special court in advance or very quickly was too bureaucratic and cumbersome and that they could not track terrorist suspects calling from or to the US.
Has the warrantless programme been successful?
It is not known, given the secrecy of the operation, but the New York Times has quoted officials as saying that "the eavesdropping programme had helped uncover a plot by Lyman Faris, an Ohio trucker and naturalised citizen who pleaded guilty in 2003 to supporting al-Qaeda by planning to bring down the Brooklyn Bridge with blowtorches". The officials also said an alleged plot involving fertiliser bomb attacks on UK targets had been exposed.
The former Speaker of the House of Representatives Dennis Hastert, a Republican, suggested that the programme had played a role in the investigation of the alleged plot to blow up airliners from Heathrow. He said in a statement, but without elaborating: "Our terrorist surveillance programs are critical to fighting the war on terror and saved the day by foiling the London terror plot."
How widespread is the eavesdropping?
The New York Times estimated that at any one time about 500 people in the US were being monitored. But as the list constantly changes, the total number wiretapped since the project started in 2002 must have risen to thousands.
The starting point was the capture of al-Qaeda operatives and their computers from which phone numbers were extracted. In turn people in contact with these numbers were subject to eavesdropping and so on in a widening circle.
How does the US compare with European countries?
European governments generally have fewer restrictions. In the UK, under the Regulation of Investigatory Powers Act 2000, it is the government not a court that authorises a wiretap. The power lies with the Home Secretary. A procedure justifying the interception has to be carried out to avoid violation of the European Convention on Human Rights and a Commissioner has oversight responsibilities, but these are limited.
In France, wiretaps are authorised by judges, though the government is suspected of by-passing them sometimes. In the Netherlands, police have powers to wiretap if the crime being investigated is serious enough. In Greece there was a scandal recently when it was found that someone unknown was tapping into mobile phones of top government ministers and security officials during the Athens Olympics.