“Fees don’t fly with us” — so goes the ad for Southwest. But is Southwest Airlines backing off its no-fee promises?

The company, which recently announced a quarterly loss (a real outlier in an otherwise profit-studded corporate history) renewed its vows to not charge for luggage fees. By not charging for the first or second bag, Southwest is really on its own in this market.

But it seems they’re starting to get jealous of the other airlines’ fee fetishes. CEO Gary Kelly hinted at future fees and optional add-ons:

“We would much prefer to explore opportunities to provide more service to customers and give them the choice to spend more money with Southwest Airlines,” he said. “Our frequent-flier program and Southwest.com both position us well to pursue that strategy.”

That’s still very vague. But it’s a disappointment to many who champion Southwest as the airline who won’t nickel-and-dime its customers.

But it shouldn’t really be a surprise. A few weeks ago, Southwest rolled out Early-Bird Check-in for a fee. (Once Southwest started suing the websites that checked you in automatically, you could see this fee coming.) But many are still saddened by Southwest’s evolution into a “normal” airline.

And if Joe Brancatelli’s recent analysis holds water, it may be a losing strategy for Southwest to pursue fees. As Joe notes, the airlines with the greatest revenue losses are the ones with the greatest reliance on bag fees and add-ons. Read the whole thing.

So is Southwest backing off on its “Fees don’t fly with us” spin? Will they be retracting ads like this one?