A federal judge has resigned from a special court set up to oversee government surveillance, FOX News confirmed Wednesday.

The judge's action followed revelations last week of President Bush's secret authorization of a domestic spying program on people with suspected terrorist ties.

Two associates of U.S. District Judge James Robertson told The Washington Post that he had submitted his resignation out of deep concern that the surveillance program Bush authorized was legally questionable and may have tainted the work of the Foreign Intelligence Surveillance Court.

Click here to read The Washington Post story.

White House press secretary Scott McClellan would not discuss Robertson's resignation or the reasons cited for his departure. "Judge Robertson did not comment on the matter and I don't see any reason why we need to," McClellan said.

Robertson, one of 11 members of the secret Foreign Intelligence Surveillance Court, stepped down from the court via a letter to Chief Justice John Roberts. He did not offer an explanation and will stay on in his role as a federal district judge for the District of Columbia.

Legal experts, however, said they know why Robertson quit.

"This was definitely a statement of protest," said Scott Silliman, a former Air Force attorney and Duke University law professor. "It is unusual because it signifies that at least one member of the court believes that the president has exceeded his legal authority."

Ruth Wedgwood, a Johns Hopkins University professor and defender of many Bush administration policies in the terror war, said that service on the special court is voluntary.

"If Judge Robertson had strong feelings that he thought would interfere with the needed objectivity, one could understand his decision," she said.

Robertson was appointed a federal judge by President Clinton in 1994. Chief Justice William Rehnquist appointed him to the FISA court in 2002 after Congress, through the Patriot Act, expanded the number of judges on the court from seven to 11.

The court is responsible for authorizing warrants for secret surveillance or searches of foreigners and U.S. citizens suspected of terrorism or espionage. According to the rules of the court, the judges are on call all the time to issue warrants. Three of the 11 judges must be within 20 miles of Washington, D.C.

Robertson, whose term was up in May, has been critical of the Bush administration's treatment of detainees at the U.S. naval prison at Guantanamo Bay, Cuba, most memorably in a decision that sidetracked the president's system of military tribunals to put some detainees on trial.

Robertson's resignation was reported hours after Vice President Dick Cheney strongly defended the surveillance program and called for "strong and robust" presidential powers.

Cheney — a former member of congress, defense secretary and White House chief of staff under President Ford — said executive authority has been eroding since the Watergate and Vietnam eras.

"I believe in a strong, robust executive authority and I think that the world we live in demands it," Cheney said.

"I would argue that the actions that we've taken there are totally appropriate and consistent with the constitutional authority of the president. ... You know, it's not an accident that we haven't been hit in four years," the vice president said, speaking with reporters Tuesday on Air Force Two en route from Pakistan to Oman.

Republicans said Congress must investigate whether Bush was within the law to allow the super-secret National Security Agency to eavesdrop — without warrants — on international calls and e-mails of Americans and others inside the United States with suspected ties to Al Qaeda.

"I believe the Congress — as a coequal branch of government — must immediately and expeditiously review the use of this practice," said Sen. Olympia Snowe, R-Maine.

Snowe joined three other members of the Senate Intelligence Committee, including Nebraska Republican Chuck Hagel, in calling for a joint inquiry by the Senate judiciary and intelligence committees.

Bush and his top advisers have suggested senior congressional leaders vetted the program in more than a dozen highly classified briefings. Several Democrats agreed said they were told of the program, but did not know the full details and had concerns.

The Associated Press contributed to this report.