Southwest Airlines

(LUV) - Get Report

is taking the lead among airlines in publicly battling the federal government's effort to impose an additional annual airport screening charge on the carrier based on a recalculation of a five-year-old security-cost analysis.

The $24 million fee would nearly double Southwest's annual screening payment -- currently assessed at $26 million -- to the Transportation Security Administration. Combined, the airlines are being asked to pay a further $104 million annually for screening, up from $319 million currently.

The other six biggest U.S. airlines say they haven't paid and haven't decided how they will respond. Domestic airlines, which have lost $40 billion over the past five years, already pay more than $3 billion a year for security charges.

Southwest, the most profitable carrier, says the new security charge is "improper," was "completely unexpected" and "made without notice or opportunity to protest." The airline last week disclosed the charge when it reported fourth-quarter earnings of $86 million.

In an interview, Southwest Legislative Counsel Tom Chapman said the airline is considering every possible remedy, including legal action.

Most of the $3 billion in annual airline security payments is made through a passenger fee up to $5 per trip, or $2.50 per flight segment, assessed under the Aviation and Transportation Security Act, which Congress approved about two months after the Sept. 11, 2001, terrorist attacks.

Besides creating the security fee, the act also required that airlinescontinue to pay the same passenger screening costs they paid in 2000. Before the attacks, carriers contracted with private security firms to screen airport passengers. Each airline was required to compute this number, according to strict accounting guidelines, and report it to the TSA. The total came to $319 million.

Since then, Chapman said, "there has been consistent grousing from the TSA about the numbers reported by the airlines. The TSA has always maintained that the airlines underreported, although there have never been any specific examples. No one at TSA ever questioned our number, and in fact, some high-ranking folk at TSA and the Department of Transportation publicly praised Southwest for the thorough job we had done and the number we reported."

At one point, Chapman said, the TSA and the Bush administration sought to increase the payments to $750 million as part of the 2005 budget bill, but Congress declined and asked the General Accounting Office to review the numbers. Last year, the GAO, the investigative arm of Congress, issued a report concluding that the actual cost was about $448 million.

The TSA, relying partially on the GAO report, concluded that the airlines were making a $104 million annual underpayment, and devised a formula to split up the bill among the carriers. Chapman said the agency determined that each carrier should pay 82 cents per passenger, even though it had previously computed Southwest's cost at 42 cents per passenger. That essentially doubled Southwest's annual fee.

American Airlines

(AMR)

, the world's largest carrier, had the second-highest new bill at $18.8 million.

"We have not paid the TSA's retroactive fee increase," said American spokesman Tim Wagner. "We are still exploring our options in regards to the increase."

Other carriers issued similar statements. Additional new charges include $14.9 million for

Delta

( DALRQ), $8.5 million for

US Airways

(LCC)

, $7.2 million for

United

(UALAQ)

and $6.7 million for

Continental

(CAL) - Get Report

.

TSA spokesman Chris White wouldn't comment specifically on Southwest, but said the new charges are legitimate and that they resulted from the GAO's impartial analysis. "They came up with their own independent numbers," he said.

"We're trying to collect past-due amounts," White said. "The fee is a vital piece of our nation's security costs. The airlines have a cost to bear, the passengers have a cost to bear and the American people have a cost to bear."

But the airline industry contends it was singled out to bear the burden of national security following the Sept. 11 attacks.

"The flag was the target, not the airlines," said Southwest's Chapman. "Security ought to be the responsibility of the government, not the airlines."

The Airline Transport Association, the industry's trade group, said it is working with its members to determine how best to respond to the new charges.

"The method TSA used to calculate the amount it claims carriers owe is inconsistent with Congressional intent," said group President James May. "We strongly oppose TSA's action."