The resignation is the latest fallout of Bush's weekend public admission that he authorized the National Security Agency (NSA) the country's super-secret electronic surveillance arm to eavesdrop on international telephone calls and electronic mail of US citizens suspected of having links with terrorist organizations including Al-Qaeda.
Bush's statement on the weekend that the secret programme did not require FISA court orders according to his reading of the Patriot Act passed after the September 11 attacks, has angered civil rights groups and lawmakers, some of whom have called for a congressional investigation.
The New York Times first revealed last week the secret NSA programme that officials said has likely involved eavesdropping on thousands of people in the United States. Bush said he expected the Justice Department to investigate the leak of such sensitive information.
Yesterday, The New York Times quoted US officials as saying that "a very small fraction" of those wiretaps and e-mail intercepts were of communications between people in the United States and were caused by technical glitches.
The revelation is likely to add fuel to the firestorm over the NSA spying programme.
Robertson's associates said the judge one of 11 on the FISA court in recent conversations said he was concerned that the information gained from warrantless NSA surveillance could have been used to obtain FISA warrants.
Source: China Daily