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Gen. William Shelton, head of the Air Force Space Command, told House members in a classified briefing earlier this month that he was pressured to change prepared congressional testimony in a way that would favor a large company funded by Philip Falcone, a major Democratic donor, congressional sources told Fox News.

Republicans have raised questions about whether the project pursued by the company, LightSquared, is being unduly expedited by the Obama administration, which has pushed for national wireless network upgrades.

The Virginia-based satellite and broadband communications company has plans to build a nationwide, next-generation, 4G phone network that many, including Shelton, think would seriously hinder the effectiveness of high-precision GPS receiver systems, a product used most commonly by the United States military.

A source familiar with the technology told Fox News that the LightSquared spectrum would be 5 billion times stronger than the military's GPS system, rendering the military's system almost useless.

"Imagine trying to have a telephone conversation while your neighbors are hosting a rock concert," the source told Fox News. "That’s the situation the military is facing."

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Shelton, in testimony Thursday before a House Armed Services subcommittee, refused to suggest that interference problems could be mitigated, as he allegedly was being pressured to say.

He did testify that testing done by various agencies responsible for military GPS positioning "demonstrated empirically that the LightSquared signals interfere with all of the types of receivers in the test."

He added that mitigation would not be possible because redesigning the equipment to filter out interference from LightSquared "would involve substantial financial cost and likely degrade the accuracy of high performance receivers, which is critical to many key GPS users."

Military training that relies on precision GPS, such as dropping ordnance, potentially could cease to exist in the United States. Many farmers who also rely on the systems would also be affected. It's estimated this system is used by as many as 1 million people.

The Federal Aviation Administration has also expressed worry about the LightSquared project. The FAA is in the process of moving from a radar based positioning system to a required GPS system for all aircraft, and it has “serious concerns” about how LightSquared may interfere with that, according to FAA spokesman Laura Brown.

A House Armed Services Committee staff member confirmed to Fox News that when asked whether he was pressured to change public testimony he had prepared for the hearing Thursday, Shelton said he was "being asked to say things he didn't agree with."

It's unclear who exactly pressured Shelton, but it's possible the individuals are in White House, Department of Defense or the Office of Management and Budget, which each approve military testimony prepared for Congress. The House staff member also told Fox News a copy of Shelton's prepared testimony was leaked to LightSquared.

Col. Kathleen Cook, a spokeswoman for Air Force Space Command, said Shelton's testimony represented his own views.

"Our testimony is reviewed appropriately by (the office of the secretary of defense), then other executive branch agencies via the established OMB process. In that process, it's common to have edit exchanges and recommendations, but I can assure you Gen Shelton's testimony was his own supported by and focused purely on documented test results," Cook said.

The White House did not respond Thursday evening to a request for comment. But The Washington Post reported that a White House official denied trying to influence Shelton's testimony.

The company also defended its work.

"We understand that some in the telecom sector fear the challenges for their business model that LightSquared presents. It's also ludicrous to suggest LightSquared's success depends on political connections. This is a private company that has never taken one dollar in taxpayer money," chief executive Sanjiv Ahuja said in a statement given to Fox News.

At the House subcommittee hearing Thursday, which focused on strategic forces and sustaining GPS for national security, Republican Chairman Michael Turner lashed out at the Obama administration for its acceptance of LightSquared proposals. He took aim at FCC Chairman Julius Genachowski, a longtime basketball buddy of President Obama, for not showing up at the hearing and for granting a waiver to LightSquared on Jan. 26.

"I trust Chairman Genachowski is doing something very important this morning if he couldn't be here to discuss the significant harm to national security that may result from the FCC's action,” Turner said.