But some critics have warned that LightSquared's base stations would interfere with GPS, and that the FCC should not have . On Thursday, 17 companies and industry associations involved with GPS formed the Coalition to Save Our GPS, which plans to fight the LightSquared initiative. The group includes GPS receiver vendor Garmin, positioning systems company Trimble Navigation, and heavy hitters including the Air Transport Association and the National Association of Manufacturers.

On Friday, Trimble Vice President and General Counsel Jim Kirkland testified before the Subcommittee on Commerce, Justice and Science of the House Appropriations Committee on behalf of the coalition.

"Initial technical analyses have shown that the distant, low-powered GPS signals would receive substantial interference from high-powered, close-proximity transmissions from a network of ground stations," Kirkland said in his testimony, according to the coalition. "The consequences of disruption to the GPS signals are far reaching, likely to affect large portions of the population and the federal government."

Kirkland told the House panel that LightSquared's network should not be deployed without a guarantee that GPS won't be affected.

When the FCC granted LightSquared's waiver, it tried to address such concerns by requiring that the carrier work with government agencies and the GPS industry to determine the potential for interference. That process is still under way.