A U.S. House of Representatives committee has stepped into the fray over startup LightSquared's planned mobile data network, and passed a bill that would block the Federal Communications Commission from spending any money granting the carrier a waiver it is seeking.

The FCC waived certain rules affecting LightSquared's network plans earlier this year, allowing the company to build a hybrid satellite and LTE (Long-Term Evolution) network as long as it tested for and solved interference with GPS (Global Positioning System).

Since then, members of the GPS industry and some lawmakers have attacked the plan and the FCC's waiver as hazardous to GPS.

On Thursday, the House Appropriations Committee passed a measure that would use Congress' control of the FCC's purse strings to stop the agency from letting LightSquared move forward.

"None of the funds made available in this Act may be used by the Federal Communications Commission to remove the conditions imposed on commercial terrestrial operations ... until the Commission has resolved concerns of potential widespread harmful interference," with GPS, said the text of the measure, an amendment to a funding bill.

The amendment came as LightSquared and the FCC came under sharp criticism at a separate Congressional hearing about the carrier's plan, in which it wants to operate a cellular network in frequencies close to those used by GPS devices. The company plans to operate its land-based network alongside a satellite system and sell services at wholesale to other carriers.

At the Congressional hearing, representatives of federal agencies and industry groups testified that LightSquared's current network plan would hobble GPS use for aviation, navigation, agriculture, defense and other purposes. Some witnesses also were skeptical about the carrier's proposal to mitigate interference by changing spectrum bands. Some also slammed the FCC for giving LightSquared a conditional waiver with too little time for debate. The oversight hearing was held by the Subcommittee on Aviation and the Subcommittee on Coast Guard and Maritime Transportation.

At the hearing, the U.S. Coast Guard and departments of Defense and Transportation reported that tests showed LightSquared's current approach caused unacceptable interference with GPS, endangering a system vital to national defense and commerce. Witnesses from the GPS industry were even more critical.

"All of the testing performed to date confirms that the LightSquared system, as currently proposed, will result in a widespread degradation of GPS receiver performance and severely limit the GPS utility as we now know it," said Philip Straub, vice president of aviation engineering at GPS equipment maker Garmin International, in written testimony. RTCA, a nonprofit advisory commission on aviation, presented the results of tests conducted with LightSquared. From those tests, RTCA concluded that aircraft would be unable to use GPS over broad areas. Other tests have led to similar conclusions.

Last week, LightSquared proposed a new plan in which it would set aside its 10MHz spectrum band that is closest to the frequencies used by GPS and instead start out by using a lower band and reduced transmission power. It has not formally submitted this new plan to regulators. Some testimony on Thursday was skeptical of this plan.

"Significant research and modeling is required to fully define this mitigation and conclusively prove whether it would achieve the desired effect," said Thomas Hendricks, senior vice president of safety, security and operations at the Air Transport Association of America.

Some critics called on Congress to scrap the regulatory process by which the FCC gave LightSquared a waiver to operate a ground-based network. The bands LightSquared plans to use were intended solely for low-power infrastructure to supplement a primarily satellite-based system, they said. After LightSquared proposed its plan last November, the FCC provided only 10 days for public comment and seven days for reply, rather than the 30 days that would be customary for such a proposal, Garmin's Straub complained.

"We call on Congress to fully investigate just how this process has proceeded to a point where the nation's GPS system is being put at risk by a single agency in the face of overwhelming government, private sector and citizen concern," said Craig Fuller, president and CEO of the Aircraft Owners and Pilots Association. He said Congress should force the FCC to have the Defense Department and Federal Aviation Administration concur before approving LightSquared's application.

In its own testimony, LightSquared laid out its new proposal and said it would not launch its network on spectrum that would disrupt GPS for a majority of users. Less than one percent of all GPS receivers in use are sensitive enough to be affected by LightSquared's network if it is operated in the lower part of the band, said Jeffrey Carlisle, executive vice president of regulatory affairs and public policy at LightSquared. He also noted that some testers, including RTCA, also saw potential in the use of the lower band.

"LightSquared will commence terrestrial commercial operations only on those portions of its spectrum that pose no risk to the vast majority of GPS users and will coordinate and share the cost of underwriting a workable solution for the relatively small number of legacy precision measurement devices that may be at risk," Carlisle wrote in his prepared testimony.

Stephen Lawson covers mobile, storage and networking technologies for The IDG News Service. Follow Stephen on Twitter at @sdlawsonmedia. Stephen's e-mail address is stephen_lawson@idg.com