Southwest Airlines is raising the price on some flights for its early bird check-ins.

Starting next Wednesday, early bird check-ins will cost $15, $20 or $25 on some flights, instead of the current $15 per person flat rate.

The new price will depend on the length and popularity of the flight.

Early bird gives travelers a better boarding position in Southwest's open seating system.

The service started back in 2009 and cost $10.