Correction: An earlier version of this article incorrectly said that FedEx and UPS were linked to a controversial labor provision included in the long-term funding bill approved by the House for the Federal Aviation Administration. The 112th Congress did not include the provision in the proposed FAA bill.

Almost 1,000 Federal Aviation Administration employees in the Washington region will face immediate furlough unless Congress extends stop-gap funding for the agency by midnight Friday.

The FAA has said about 4,000 of its 32,000 workers nationwide would be furloughed, and the Transportation Department said Thursday that 975 would be people based in the Washington region. The furlough would also affect construction workers under FAA contract on airport projects.

With the clock ticking down Thursday, the possibility of a compromise that could save the FAA from a temporary partial shutdown grew less likely.

“We are going to be forced to furlough valuable FAA employees unless this situation is resolved quickly,” FAA Administrator Randy Babbitt said Thursday. “These employees do everything from getting money out the door for airport construction projects, to airport safety planning and NextGen research. We need them at work.”

Air traffic controllers would remain on the job, and Transportation Secretary Ray LaHood sought to reassure the flying public that air safety will not be compromised if the stalemate results in a partial shutdown.

“If Congress does not pass a clean extension, $2.5 billion for airport projects and thousands of construction jobs will be vacated as a result,” LaHood said. “Congress has been able, in a very short period of time, to have passed a clean extension. We urge Congress to pass a clean bill.”

Funding extensions normally are a routine matter when Congress reaches an impasse over comprehensive long-term spending bills. The one under consideration would be the 21st for the FAA since the last funding package expired in 2007.

But this extension has been put into doubt because the House transportation committee chairman, John L. Mica (R-Fla.), inserted additional language in the extension bill that would curtail a program that subsidizes air service to rural airports.

That has been denounced in the Senate, where the commerce committee chairman, Sen. John D. Rockefeller IV (D-W.Va.), said he plans to introduce his own extension bill, and by the White House, which demanded Wednesday that Congress come up with a “clean” extension unburdened by controversy.

Unless both houses pass identical extension bills before the furlough deadline, a shutdown seems likely because finding compromise on conflicting bills appeared impossible before midnight.

The House and Senate passed longer-term funding reauthorization bills for the FAA this year, but although Mica has talked with his Senate counterparts, a conference committee has yet to be called to resolve significant differences in funding levels and the number of years covered by the bills.

“The House has been and continues to try to get a resolution,” said a House GOP staff member familiar with the talks who was not authorized to speak publicly. “This is about negotiation. We’re not saying it’s my way or the highway. We’re kind of worried that the Senate will be happy with more extensions so they don’t have to deal with these tough issues.”

The House bill also curtails a federal subsidy program that provides commercial air service to small-town airports. The program was created in 1978 after airline deregulation, with an expected 10-year life span. Three presidents — Ronald Reagan, Bill Clinton and George W. Bush — later targeted it for elimination, but it has been extended by Congress and now costs about $163 million a year.

The Senate bill would cut service to 10 airports that are within 90 miles of a larger airport. But the Senate is balking at language Mica added to the House extension legislation that eliminates service to three airports where the federal subsidy is more than $1,000 per passenger.

“Every ticket at the Ely, Nevada, airport is underwritten $3,720 by federal taxpayers,” Mica said. “It is now up to the Senate to pass this [extension] bill and not shut down FAA programs over a little provision that eliminates huge government subsidies to just three small airports.”

Mica said the Essential Air Service program also pays $1,563 per passenger for commercial service into New Mexico’s Alamogordo/Holloman Air Force Base and $1,358 per passenger for flights to Glendive, Mont.

A final disagreement between the two long-term bills is over the number of flights that should be allowed at Reagan National Airport and how new slots should be allocated.