(AP) -- The era of free checked suitcases on JetBlue has come to an end.

The airline proudly proclaimed itself a holdout on fees for years, allowing passengers to check one bag for free. Now it will charge up to $25 for checked luggage.

The move leaves Southwest Airlines as the only major U.S. carrier not to charge a bag fee.

JetBlue Airways had announced the change in November but didn't detail how it would be implemented until Tuesday. The fee only applies to new bookings; existing reservations still get one free bag.

Passengers will pay less if they plan ahead. Those with the cheapest tickets will pay $20 each way if they check in online or at a kiosk. The fee jumps to $25 if they go to the counter. A new fare class that costs about $15 extra each way would include one free bag.

Fees for a second checked bag and reservation changes are being lowered.

The airline plans to reinvest the millions of dollars it will collect from bag fees into new seats and TVs, according to Marty St. George, JetBlue's executive vice president of commercial products and planning.

"Some of these changes are going to help pay for what's the biggest product upgrade JetBlue has had in the history of the company," he told The Associated Press in advance of the announcement.

Under pressure from investors and Wall Street analysts, JetBlue has been slowly adopting the practices of other airlines. It has launched and then expanded a first class product called Mint. It has reduced legroom on some planes to fit more passengers. Now it is charging for bags, something other carriers started doing in 2008.

The New York-based airline still stands out in other ways. By the end of next year, it will offer free Internet on all its Airbus A320 and A321 jets. Passengers also get free access to more than 100 channels of live satellite TV and radio and JetBlue still has more legroom than its competition.

JetBlue doesn't have a fixed bag fee like other airlines. Instead, it has rolled out three new fare classes. The cheapest, called Blue, doesn't include a checked bag -- although passengers can always add one later at a higher cost. The next fare, Blue Plus, includes one free checked bag, more frequent flier points and lower fees if passengers want to make changes to the reservation. The most-expensive tier is called Blue Flex and comes with two free checked bags and allows changes without penalty.

The fare difference between Blue and Blue Plus will change based on route and demand but should be "about $15," according to JetBlue. Blue Flex would cost about $100 more each way than the cheapest tickets and is fully refundable.

Online travel agencies like Orbitz, Priceline and Expedia, will -- for the foreseeable future -- only sell the cheapest fares, those that don't include a checked bag. Passengers will still have to pay at the airport for their checked bags but St. George notes that about 75 percent of passengers book directly with JetBlue.

Some fees are being cut. The charge for a second checked bag will drop from $50 each way to $35. JetBlue used to charge $75 to $150 to make changes to a reservation, based on the price of a ticket. That fee is dropping to $70 to $135 for the cheapest tickets and $60 to $120 for the Blue Plus fares.

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Scott Mayerowitz can be reached at http://twitter.com/GlobeTrotScott.