Privacy watchdogs are urging the nation's top law enforcer to launch a new investigation into Google Inc. after the Federal Communications Commission did not find evidence that the Mountain View, Calif., company broke eavesdropping laws in collecting Internet data from millions of unknowing U.S. households.

The Electronic Privacy Information Center, or EPIC, the Washington advocacy group that filed the original complaint with the FCC over Google's controversial data-collection practices, sent a letter Monday to U.S. Atty. Gen. Eric H. Holder Jr. calling the FCC's probe insufficient.

"By the agency's own admission, the investigation conducted was inadequate and did not address the applicability of federal wiretapping law to Google's interception of emails, user names, passwords, browsing histories and other personal information," EPIC's Executive Director Marc Rotenberg wrote in the letter. "Given the inadequacy of the FCC's investigation and the law enforcement responsibilities of the attorney general, EPIC urges you to investigate Google's collection of personal Wi-Fi data from residential networks."

Rep. Edward J. Markey (D-Mass.), senior member of the House Energy and Commerce Committee, called for Congress to hold a hearing "to get to the bottom of this serious situation."

"The circumstances surrounding Google's surreptitious siphoning of personal information leave many unanswered questions," he said Monday.

The FCC said late Friday that it would fine Google $25,000 for obstructing its investigation of the search giant's Street View service. Privacy advocates dismissed the proposed penalty as negligible for a company that had nearly $38 billion in revenue last year and stands accused of snooping on people's private information and stonewalling investigators.

As part of its Street View project, Google sent specially equipped cars into U.S. streets to snap photos of homes and buildings in an ambitious attempt to map the country, block by block. But from May 2007 to May 2010, Google also collected sensitive information from unencrypted home wireless networks, including emails, passwords and search histories.

News of Google's snooping caused an uproar when it was disclosed in 2010, leading the FCC to launch its investigation. But in announcing its proposed fine last week, the agency said it did not find proof that Google had violated the federal communications law that bans electronic eavesdropping.

The FCC said its probe ran into two insurmountable hurdles: There is no precedent to apply the FCC law to unprotected Wi-Fi networks, and the agency did not uncover enough evidence that Google had violated federal rules.

Google, which has apologized for the data collection, denied the FCC's assertion that the company did not cooperate with the agency. It has 30 days from the FCC's April 13 report to contest or pay the proposed fine.

"We disagree with the FCC's characterization of our cooperation in their investigation and will be filing a response," a Google spokeswoman wrote in an emailed statement.

Ryan Calo, director of privacy at Stanford's Center for Internet and Society, called the proposed $25,000 fine a "slap on the pinkie..."