Don’t tell that to Rachel Truman. Some ambitious ticket agent charged her $100 to check two boxes of frozen fish she caught this summer in the Icy Strait near Juneau–a lot, considering she paid only $500 for her ticket. The 25-year-old cook from Las Vegas thinks the fees are “kind of bogus.” Next time, says Truman, “maybe I won’t fly with them.”

The conflict between cash-strapped airlines and their weary customers has never been so heated. Major airlines–hemorrhaging billions of dollars from the weak economy, high labor costs and terrorist attacks–are introducing a slew of new fees in an attempt to return to profitability. In the past few weeks they have announced new rules that make it more expensive to change flight plans, carry extra bags and fly standby. Customers–already fuming over crowded airplanes, fewer flights and security delays–are apoplectic. “Consumers feel cornered,” says Colorado-based aviation consultant Michael Boyd. “And cornered critters come out fighting.”

Angry reaction to the new rules startled some big airlines. In August struggling US Airways announced that customers with low-fare, nonrefundable tickets would no longer be able to fly standby if they wanted to change flights at the last minute, and couldn’t use their mileage toward elite status in its frequent-flier program. But the company received so many angry letters that it was forced to retrench only a week later.

Yet other changes stuck. Some airlines, including US Airways and Northwest, will soon void any ticket if you skip your flight and fail to notify them by takeoff. Others, like American and United, insist you rebook by midnight the same day–for a fee of $100. The luxury of a paper ticket will now cost as much as $25. Newly enforced oversize-bag fees can run almost $300 per bag. And starting next year, most airlines will charge $100 more to fly standby. One notable exception: low-fare juggernaut Southwest will still let you change dates and fly standby free of charge.

Airlines consider the changes long overdue. While passenger traffic is still about 10 percent lower than last year, revenues at some carriers are down more than 20 percent, due in part to low-cost upstarts and fewer high-fare business travelers. All year the big airlines have quietly upped fees in –an effort to close that gap. In August Continental announced that customers would have to ask for full cans of soda and breakfast knives if they wanted them. Penny-pinching like this is nothing new: in the 1980s American Airlines boasted that it could save $40,000 each year by giving customers one olive, instead of two, in their salads. But this autumn’s changes could be the start of something far more ambitious. Boyd says he knows of at least one major airline that is mulling charging extra for all checked bags.

How can you keep the rules straight and avoid new charges? Leisure travelers should grill reservation agents about the new math. And last week some corporate travel agencies announced plans to warn customers when their tickets are about to expire. Rosenbluth International (rosenbluth.com) introduced what it calls SmartTicket, a system of e-mail alerts to keep clients informed about their ticket deadlines. Traveling light will save extra baggage fees. And please–if you must bring home a moose head, consider UPS.