(CNSNews.com) - Former Vice President Al Gore got the ball rolling on Monday, when he called for a special prosecutor to investigate President Bush's secret, warrantless wiretapping program; and now a liberal advocacy group is trying to keep up the momentum with a petition drive.

"Breaking the law to spy on American citizens is a very serious abuse of power, but many members of Congress think people will let it slide," said MoveOn.org Political Action.

The group launched a petition drive on Wednesday, asking the U.S. attorney general to appoint a special prosecutor "to find out the facts" and ask Congress to hold a "real investigation into what happened."

MoveOn.org Political Action said it hopes to gather 250,000 signatures on its petition, to be delivered to Congress just before it holds hearings on Bush's wiretaps in early February.

Speaking on Monday, Al Gore said, "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 persistently."

Gore accused the Bush administration of undermining "the American values we hold most dear" through a "breathtaking expansion of executive power."

(The Republican National Committee, responding to Gore's speech, noted that "While the president works to protect Americans from terrorists, Democrats deliver no solutions of their own, only diatribes laden with inaccuracies and anger.")

But even some conservative leaders have questioned President Bush's decision to authorize the National Security Agency to "violate domestic surveillance requirements" outlined in federal law.

Earlier this week, former Republican Rep. Bob Barr, speaking on behalf of a conservative group called Patriots to Restore Checks and Balances, urged Congress to hold hearings on the matter.

As Barr noted, "federal law still clearly states that intelligence agents must have a court order to conduct electronic surveillance of Americans on these shores. Yet the federal government overstepped the protections of the Constitution and the plain language of FISA to eavesdrop on Americans' private communication without any judicial checks and without proof that they are involved in terrorism."

'Nervous' White House

MoveOn.org has called Al Gore's speech "important, powerful, inspiring and 'reality-based.'" Moreover, the group said, the speech is "making President Bush nervous," sending the White House into "full-blown spin" to defend against it.

'They're in deep trouble on this -- and they know it," the press release said.

The liberal group noted that even the non-partisan Congressional Research Service -- the research arm of Congress -- released a report on Wednesday, indicating that the White House program "conflicts with existing law."

The CRS report, done at the request of Rep. Jane Harman (D-Calif.) said the Bush administration should have been more forthcoming with Congress: The decision to tell only a handful of senior lawmakers about the secret program "would appear to be inconsistent with the law, which requires that 'congressional intelligence committees be kept fully and currently informed of all intelligence activities," the report said.

According to press reports, the CRS report was written by Alfred Cumming, a former Democratic staff director of the Senate Intelligence Committee.