President George W. Bush says the program is needed in the war on terrorism; opponents say it oversteps constitutional boundaries on free speech, privacy and executive powers.
The 6th U.S. Circuit Court of Appeals' ruling by a unanimous three-judge panel allows the program to continue during an appeal that could take months.
In their brief order, the judges said they balanced the likelihood of success of an appeal, the potential damage to either side and the public interest.
U.S. District Judge Anna Diggs Taylor in Detroit ruled on Aug. 17 that the program targeting communications between people in the United States and people overseas with a suspected link to terrorism is unconstitutional. She refused Sept. 28 to postpone her ruling during appeals, but gave the government a week to ask the 6th Circuit to halt it from taking effect.
The Justice Department had urged the appeals court to allow it to keep the program in place while it argues its appeal, claiming that the United States faced "potential irreparable harm."
"The country will be more vulnerable to a terrorist attack," the government motion said.
The government is challenging Taylor's ruling that the effort, which it calls the Terrorist Surveillance Program, violates the rights to free speech and privacy, as well as the separation between the executive, legislative and judicial branches enshrined in the constitution.
The White House says the surveillance is a key tool in the fight against terrorism and has already helped prevent attacks.
The American Civil Liberties Union filed the suit on behalf of journalists, scholars and lawyers who say the program of warrantless wiretaps of phone and Internet communication has made it difficult for them to do their jobs because they believe many of their overseas contacts are likely targets. Many said they had been forced to take expensive and time-consuming overseas trips because their contacts would not speak openly on the phone or because they did not want to violate their contacts' confidentiality.
Similar lawsuits challenging the program have been filed by other groups, including in New York and San Francisco. Taylor, appointed by former President Jimmy Carter, a Democrat, was the first judge to rule the National Security Agency program unconstitutional. The issue could wind up before the U.S. Supreme Court.
Bush has said he strongly disagrees with Taylor's August decision, saying those who support her view "simply do not understand the nature of the world in which we live."
"This country of ours is at war," Bush said the day after her ruling. "And we must give those whose responsibility it is to protect the United States the tools necessary to protect this country in a time of war."
In her ruling, Taylor said the Bush administration appeared to be saying the president had the "inherent power" to violate laws of Congress.
"There are no hereditary kings in America and no powers not created by the Constitution. So all 'inherent powers' must derive from that Constitution," Taylor wrote in a 43-page opinion. "The public interest is clear, in this matter. It is the upholding of our Constitution."
The ACLU says the 1978 Foreign Intelligence Surveillance Act, which set up a secret court to grant warrants for such surveillance, gave the government enough tools to monitor suspected terrorists.
"Every time the NSA engages in warrantless wiretapping, they are violating the law and the United States Constitution," ACLU attorney Melissa Goodman said last month.
But the government says it cannot always wait for a court to take action. It says the NSA program is well within the president's authority, but to prove that would require revealing state secrets.