Millions of dollars in U.S. airport taxes went uncollected Sunday while thousands of federal workers were out of work for a second day, following Congress' failure last week to pass a bill keeping the country's aviation authority running.

Some 4,000 workers with the Federal Aviation Administration (FAA) were told to stay home beginning Saturday, after congressional authorization for several FAA programs expired at 12:01 a.m. that day.

As a result, FAA employees in 35 states, as well as in Puerto Rico and Washington, DC are furloughed without pay, U.S. officials said.

Observers said the disabled federal agency foreshadows what could happen around Washington and across the country if Congress fails to reach a deal in its separate negotiations with the White House over a debt ceiling, as it tries to avert a catastrophic federal default before an August 2 deadline.

In a weekend statement, the FAA said efforts are underway to get authorization for the agency renewed as quickly as possible.

"We are working diligently with Congress to resolve this unfortunate situation, and apologize for the hardship this situation may cause for our employees and our stakeholders," the agency said.

The failure to reach a deal has resulted in a mini-bonanza for airlines.

With the FAA no longer authorized to collected the 7.5 percent federal excise tax usually levied on each ticket, or the US$3.70 tax applied to each flight segment, many airlines have simply pocketed those proceeds.

Analysts said the airline industry could benefit by US$25 million each day that FAA reauthorization is not granted.

In a statement, Transportation Secretary Ray LaHood expressed disappointment that Congress adjourned last week without passing an FAA reauthorization extension, leaving the agency in limbo.

As a result, the statement said "many states will have to bear a significant economic burden and many airport projects will be halted."

"Because of their inaction, states and airports won't be able to work on their construction projects, and too many people will have to go without a paycheck," he said.

"This is no way to run the best aviation system in the world," the U.S. transportation chief said.

But U.S. Senator Tom Coburn on Sunday slammed the "waste and duplication" in the federal government for lawmakers failing to reauthorize the FAA's mandate, telling NBC's "Meet The Press" that they weren't approving the agency "because they continue to want to subsidize irresponsible and wasteful behavior."