That extra piece of luggage is going to cost you.

Starting May 5, US Airways will begin charging passengers $25 for a second checked bag, matching a recent policy change by rival United Airlines. The move illustrates the shift in many industries to an a la carte model in which customers pay only for the services they want -- or can't avoid.

"It's a sign of the times," said David Stempler, president of the Air Travelers Association, a trade group representing U.S. passengers. The big air carriers "are unbundling their services and may start charging for each of them -- extra bags, priority seats, food, maybe drinks, pillows and blankets."

US Airways -- which already charges $7 for meals in coach, $15 to book a reservation over the phone, $20 to buy a ticket at the airport and $2 for curbside check-in -- will assess the new checked-baggage fee on each leg of a round-trip flight, totaling $50 for both ways. The extra charge for a third checked bag is now $100, up from $80. Also still in place is an overweight charge of $50 for any suitcase heavier than 50 pounds and $100 if the luggage is 70 pounds or more.

The new second-bag policy applies to flying that takes place on or after May 5 and covers all flights within the United States, and to and from Canada, Latin America, the Caribbean and Europe. Customers who purchased tickets before today are exempt from the charge, as are Dividend Miles Preferred or Star Alliance Silver and Gold members, US Airways employees, members of the military and any customers checking such "assistive devices" as walkers, crutches and wheelchairs.

The largest carrier at Pittsburgh International Airport played down the impact of its new policy, claiming that just 8 percent of its customers check two or more bags, while attributing the change to the soaring price of oil. Higher fuel prices are expected to add $800 million to US Airways' expenses in 2008, according to a memo US Airways President Scott Kirby distributed to employees and the press yesterday.

While US Airways could raise fares to offset the fuel increases, that might drive passengers to rival carriers at a time when there are too many seats chasing too few passengers, he argued.

"Some critics may call this another example of airline customers being 'nickel-and-dimed' for services that used to be provided as part of the flying experience -- food, entertainment, and now bags," he wrote. "But the airline industry of 2008 is very different from the industry of 1998 or 1988, and we have to be realistic -- and innovative -- about our product. I suspect that this will be a year when we see a lot of change in the industry -- mergers, acquisitions, and more 'un-bundled' services rather than a 'one product fits all' approach to our business."

The same is occurring in other industries. Hotels are charging extra for bottled water, use of the gym and the phone while rental car companies are tacking on fees for satellite radio and navigation systems. Mr. Kirby cited both examples in his memo yesterday.

"These business models reflect the reality that services cost money," he wrote, "and those who want and use them should pay for them."

Airlines have been chipping away at amenities and complimentary features for decades, a trend spawned by Congress' deregulation of the industry in 1978, which forced carriers to compete on price and find ways to save a few bucks here and there. American Airlines boss Robert Crandall bragged two decades ago about saving $40,000 after eliminating black olives from salads. Delta Air Lines in the 1990s cut a single lettuce leaf from meals and saved $1.4 million a year. Many airlines also began charging for alcoholic drinks.

But the changes accelerated after the Sept. 11, 2001, attacks, an event that crippled the industry and forced several troubled carriers to seek the protection of bankruptcy court.

Complimentary snacks and meals were among the frills to go after Sept. 11. America West Airlines, the carrier that merged with US Airways in 2005, was the first major airline to take the risky move of charging for meals in coach. US Airways did the same in 2003, as did many other big carriers. A cinnamon raisin turkey ham sandwich, a walnut chicken salad or a pastrami and roasted pepper sandwich now costs you $7 in coach, while a "cafe' snack box" of crackers, fruit bar, fruit and nut mix, cookies and chicken salad goes for $5. Beer, wine and cocktails are all $5. The meals are served only on flights over 3.5 hours, between the hours of 5 a.m. and 8 p.m. Snack boxes are available on flights over 2.5 hours.

Post Sept. 11, the only free services remaining are meals in first class and on transatlantic flights, pillows and blankets, nonalcoholic beverages and a bag of pretzels, "if you're lucky," said frequent flier Jim Johnston, a member of Frequent Flyers Organized and Committed to US Airways Success.

And what remains unsettling for passengers is that customer service continues to suffer, despite the array of new fees and charges. Airlines lost a record number of bags in 2007, and US Airways was the worst performer in the industry, finishing first in customer complaints and last in mishandled bags -- 8.47 per 1,000 passengers.