Two U.S. civil liberties groups have filed lawsuits in federal court seeking to stop the domestic spying program authorized by President Bush shortly after the 2001 terrorist attacks.
The lawsuits were filed by the American Civil Liberties Union and the Center for Constitutional Rights.
Both groups contend that President Bush exceeded his authority when he authorized the National Security Agency to monitor international phone calls and e-mails of American citizens suspected of links with terrorists without obtaining a court warrant.
The lawsuits were filed in New York and Detroit on behalf of defense lawyers, journalists and academics who believe their communications with people in the Middle East are being monitored by the National Security Agency.
Anthony Romero is the executive director of the American Civil Liberties Union.
"We believe it to be unconstitutional and illegal because of the absence of any judicial approval in accessing information on American citizens," said Mr. Romero. "We also believe it is illegal because Congress failed to authorize such a program."
At the White House, presidential spokesman Scott McClellan defended the domestic eavesdropping program as an essential tool in the war on terror.
"I think that the frivolous lawsuits you reference do nothing to help enhance civil liberties or protect the American people, and that is what those are," he said. "In terms of this authorization, again, it is a vital tool and it is limited."
The filing of the lawsuits came one day after former Vice President Al Gore accused the president of breaking a 1978 surveillance law by authorizing domestic eavesdropping without a court order.
"What we do know about this pervasive wiretapping virtually compels the conclusion that the president of the United States has been breaking the law, repeatedly and insistently," said Mr. Gore.
Gore has called for a criminal investigation into the president's domestic spying program.
Bush spokesman McClellan says the former vice president is guilty of hypocrisy, noting that the Clinton-Gore administration argued that physical searches of criminal suspects without a warrant were justified.
A 1978 law makes it illegal for the government to spy on Americans without first getting approval from a secret federal surveillance court.
But U.S. Attorney General Alberto Gonzales argues that Congress granted President Bush broad powers to wage a war on terror in the aftermath of the September 2001 terrorist attacks.
"We believe the authority, the legal authorities, are there and that the president acted consistent with his legal authorities and in manner that he felt was necessary and appropriate to protect this country against this new kind of threat," he said.
Several opposition Democrats have criticized the domestic spying program as a presidential abuse of power. Many Republicans have defended the monitoring program as an essential tool in the war on terror.
But some Republicans are questioning whether the president was within his rights to authorize the eavesdropping without first getting approval from Congress.
Republican Arlen Specter chairs the Senate Judiciary Committee. He told ABC's This Week program that he plans to hold hearings on the issue next month.
"We are not going to give him a blank check and just because we are of the same party does not mean we are not going to look at this very closely," he said.
Recent public opinion polls suggest Americans are about evenly divided on whether the president's domestic eavesdropping program is justified during a time of war.