Two Republican lawmakers urged the top U.S. communications regulator to resist political pressure for allowing broadband start-up LightSquared to deploy a network that could interfere with the global positioning system.

Representative Thomas Petri and Senator Charles Grassley sent a letter on Thursday to the Federal Communications Commission saying a single company should not be allowed to threaten such critical national infrastructure.

It is odd that the FCC has pegged the hopes of expanding broadband access on such a controversial proposal by a single applicant, said the letter to FCC Chairman Julius Genachowski.

Hedge fund manager Philip Falcone's start-up came under fire after months of testing found its original plan for a high-speed wireless network would interfere with GPS devices that are used by the military, and in aviation, agriculture, construction and other civilian applications.

Deployment of the network depends on regulatory approval from the FCC, which is conducting additional testing on LightSquared's proposal to ensure GPS operations would not be affected.

We urge you to resist political pressures to grant LightSquared an authorization that could jeopardize the nation's unique spectrum resource -- GPS, the lawmakers said.

Seven House of Representatives Republicans earlier in the week sent a letter to the White House, asking for records of its communications with LightSquared and about reports that senior administration officials were pressured to change their congressional testimony to look more favorably on LightSquared.

Genachowski told reporters after an agency open meeting on Thursday that the FCC's review of LightSquared's proposal has been fact- and engineering-based, involving all the stakeholders.

That's our obligation, that's what we've done and that's what we'll continue to do, he said.

The broadband start-up has become one of billionaire Falcone's riskiest and most high-profile bets.

LightSquared intends to invest $14 billion over the next eight years to build its network, and aims to sell wholesale wireless services to companies which would then resell the service under their own brand names.

The national network could serve roughly 260 million people using satellites and land-based signals. The interference issues have arisen over the land-based portion of the network.

The company in June unveiled a new plan for deploying its network that uses a different block of wireless airwaves that is farther away from the GPS band.

LightSquared has announced a partnership with GPS technology company Javad GNSS Inc to develop a system that it believes will eliminate interference to high-precision GPS devices that its June proposal did not address.

(Reporting by Jasmin Melvin; Editing by Tim Dobbyn)