Southwest Airlines' early bird check-in changes includes one of three fees dependent length and popularity

DALLAS, Texas -- Southwest Airlines is about to start hitting customers with higher fees to check in early for flights.

The Dallas-based carrier charges a flat $15 for early bird check-in so travelers can get better boarding positions for Southwest's open seating system.

Starting on Aug. 29, though, that flat fee will change to one of three fees: $15, $20 or $25 per one-way flight.

The price will depend on the length and popularity of early bird check-in for each way on the flight.

Southwest says as early bird check-in increases in popularity, it wants to protect the value it offers its customers.