That appears to be another fee in addition to PFCs. Remember PFCs are user fees capped at $4.50 per airport departure or connection and are added to your base ticket price and you can see it in action as you add sectors for mileage runs.

Here are some current fees (SEA is $4.50):

http://www.southwest.com/travel_center/pfc.html

Apparently participation is up to the state, or owner of the airport.

http://www.akrepublicans.org/pastleg...y102091999.htm

House Transportation commitee brief on ths whole programme:

http://www.house.gov/transportation/...06-03memo.html