NEW YORK (MainStreet) – It was only a matter of time: Airline fees have begun replicating at an exponential rate.

Spirit Airlines, which last year started charging passengers $30-$45 for carry-on bags, has found a new way to extract money from people who want to bring things with them when they fly. For all tickets booked on or after March 23, Spirit will now charge passengers a fee for not paying their baggage fees far enough in advance.

Yes, you heard that right: A fee for not paying a fee early enough.

The fee for your first checked bag is normally $28 for domestic flights and $33 for international flights – if you pay for the bag in advance. But if you pay the luggage fee online within just 24 hours of your flight, the airline will take an additional surcharge of $5. And if you pay your baggage fees by phone or at the airport within 24 hours of the flight, the surcharge rises to $10. So if you’re flying internationally and forget to pay your fee in advance, you’ll be charged $43 for your (lack of) trouble.

The surcharge also applies to carry-on bag fees. If you have a carry-on bag that won’t fit under the seat in front of you, you’ll be charged $30, but that can be as high as $40 if you wait until the last minute. Our advice is to measure your bag in advance – according to the airline the under-seat space is 16x14x12 inches, and anything bigger than that will incur the fee.

To be fair to Spirit, it’s not the first airline to charge a fee-paying fee. Both Delta and Continental, for instance, charge an extra $2 on top of their $23 checked bag fee if you wait until you get to the airport to pay it, for instance. But Spirit looks to be charging the highest surcharge of the major carriers.

But the worst part is the spin: Spirit is calling the new penalty an “Early Bird Discount,” as if to imply that they used to charge a fixed fee for bags and will now be deducting from that fee for people who pay early. Of course, the opposite is true: They used to charge a fixed fee, but now people who pay that fee at the last minute will be charged another fee.

Indeed, right below the description of the “Discount” on the airline’s baggage fee page it says that “Customers who booked their travel before March 23, 2011, will not be charged the additional bag fees listed above.” So even as the marketing department  tries to call it a discount, the airline’s own website calls a spade a spade and refers to it as an “additional bag fee.”

So really, nobody’s getting a discount at all. It’s just another fee, dressed up Bugs Bunny-style to look like a pretty discount.

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