Nearly 5,000 Transportation Department (search) workers face a furlough on Monday, a possible result of two senators using an expiring highway bill to force House Republicans to accept a two month extension of an independent investigation of the Sept. 11 terror attacks.

"We all have a choice here to make," said Sen. John McCain, R-Ariz., who along with Sen. Joe Lieberman, D-Conn., was using the highway bill as leverage to win an extension for the National Commission on Terrorist Attacks Upon the United States (search), which is scheduled to finish its work on May 27.

He said the choice was between "minor" disruptions in highway projects and "telling the families of those who died on 9/11 that the commission will not be able to complete its work."

President Bush has agreed to extend the commission's work until July 27, but efforts to legislate that action have met resistance among House Republican leaders, including Speaker Dennis Hastert, R-Ill.

"There are people that have great concerns about extending the 9/11 commission on our side of the rotunda," House Majority Leader Tom DeLay, R-Texas, said Thursday. One of those concerns is that the findings of the commission, which is studying the nation's preparedness before the attacks and its response, may come too close to the presidential election.

Former Gov. Thomas H. Kean (search) of New Jersey, the commission's chairman, said getting an extension was urgent. Without it, he said, "means certain research we're planning to do won't get done, and certain trails we won't be able to follow. Some of our conclusions won't be as informed."

Lieberman said the commission had not been able to complete its work because of foot dragging by the administration and stalled highway programs would "pale in significance to not giving the commission the extra time it needs."

Senate Majority Leader Bill Frist, R-Tenn., who supports extending the commission's life, on Friday sought to meet the demands of the two senators by quickly bringing up for a voice vote a bill, approved by the Senate Intelligence Committee on Thursday, that authorizes the two-month extension. But McCain and Lieberman wanted that extension on a bill that the House could not ignore.

The existing highway and public transit spending law expires on Sunday, and without a temporary extension the Transportation Department may have to furlough about 5,000 workers, spokesman Robert Johnson said.

"If the Senate doesn't pass an extension by Sunday night, then today would be their last day on the job," he said.

Johnson said affected departments are the Federal Highway Administration (search), Federal Motor Carrier Safety Administration, the Bureau of Transportation Statistics and the National Highway Traffic Safety Administration (search).

"There wouldn't be anyone working with states on their federal highway projects, there wouldn't be anyone to assist with truck inspections along the borders, there wouldn't be anyone to handle consumer complaints about household goods movers, there wouldn't be anyone at NHTSA to deal with their various safety programs," he said.

The House and Senate are now trying to work out differences on a major new highway bill that would outline spending over the next six years. The Senate recently approved a $318 billion bill, which the White House has threatened to veto, saying it shouldn't go above the president's $256 billion proposal.

The House has yet to take up its bill, but is expected to press for at least the amount passed by the Senate.

House Transportation Committee Chairman Don Young, R-Alaska, late Thursday won House approval of a two-month extension of the highway program to keep projects going while the negotiations continue on the new bill.

McCain and Lieberman are blocking the Senate version of the two-month highway bill extension.

Sen. Kit Bond, R-Mo., a senior member of the Senate Environment and Public Works Committee, criticized the two senators, saying they were "seeking to hold hostage the whole highway program in the United States." He said their action would shut down contract authority and payments for work already contracted by the states.

White House press secretary Scott McClellan on Friday said Bush, who has agreed to meet privately with the commission, agreed to its extension. He said assertions that Hastert was doing the White House bidding in opposing the extension was a "silly idea."