(CNN) -- Want to be the first to board a Southwest Airlines flight?
It'll cost you.
Starting 45 minutes before a flight's departure, any remaining spots in the airline's "A" boarding group can now be purchased for a $40 fee payable by credit card.
"Offering customers the option to improve their boarding position on day of travel is one more way we can offer the travel experience that best fits their needs," said Kevin Krone, Southwest Airlines vice president of marketing, sales and distribution, in a press release.
The airline doesn't assign seats but it does give certain fliers the right to board before other fliers. They include people who buy Business Select Fares, Rapid Rewards Members with A-List and A-List Preferred status, and EarlyBird Check-In customers. Those early boarders have first crack at the best seats and overhead bin space.
Got that? Southwest's boarding practices are unusual enough compared to other airlines that they've got an online tutorial.
"This is yet another of several recent attempts by Southwest to add peripheral fees so that it can raise revenues without tarnishing its image," wrote Brett Snyder, president of The Cranky Flier, in an e-mail. "Southwest's elite travelers won't like that people can buy their way to the front of the line, but it will be welcomed by those at the back. This is the first effort Southwest has made to allow people to better their position once they know their boarding number."
The airline does offer two free pieces of checked baggage, so there's no need to fight over overhead space unless you need it.
AirTran Airways, a wholly-owned subsidiary of Southwest Airlines, is not charging this fee. However, Southwest continues its program of repainting AirTran planes in Southwest colors, putting them back into service as Southwest flights and charging Southwest fares and fees, a Southwest spokeswoman confirmed.