Some passengers traveling on Southwest Airlines (LUV) will now have to pay more to board first.

Effective immediately, the airline will charge passengers in select markets $50 each way for upgraded priority boarding. This is up from the previous rate of $40. Upgraded boarding can be purchased at the airport on the day of travel to secure one of the first 15 spots in boarding group A.

On Southwest, seats are not assigned at booking. Instead, travelers are placed in groups based on when they check in for the flight. Group A boards first, followed by B, then C. Those in group C usually end up getting a middle seat and must fight for space in the overhead compartment.

“Every few years, we review the price of our services in order to align with market and operational conditions as well as uphold the quality of our offerings,” a Southwest spokesperson told Yahoo Finance. “Southwest has increased the price of purchasing Upgraded Boarding to $50 in a handful of our markets while others remain $30 or $40 for the service.”

Southwest will not specify which airports will see the fee jump because any number of factors can influence the cost.

Unlike other airlines, Southwest tends to avoid mandatory fees. Customers don’t incur a fee for changing their reservation (usually $150 on other airlines), and passengers can check their first two bags of luggage for free (typically $25 to $50 on other airlines.)

Instead, many of Southwest’s fees are optional, though at times it can feel like the only way to have a comfortable flight is to pay for it. For instance, travelers can opt to pay $15 for Southwest’s Early Bird check-in, which lets them check in for their flight before the typical 24-hour window. This improves their chances of landing in boarding group A or B. If you don’t want to do this, there’s a good chance you’ll end up in dreaded group C with a middle seat, even if you checked in on time.

For consumer advocate Chris Elliott, Southwest upping their optional fee for boarding early is typical, but it could be worse. “Like other airlines, Southwest is always looking for ways to increase its ancillary revenues,” he told Yahoo Finance. “In a perfect world, there would be no fees, but I like Southwest way better than the other big carriers, which don’t give you much choice about paying extra.”

Airlines profit from seat selection fees

Of course, Southwest isn’t the only airline charging extra for seat selection or early boarding privileges. Most major carriers charge passengers to select their seat.

Passengers on American, Delta, and United are charged anywhere from $9 to $75 or more per segment for what is considered preferred seating. These are seats located on the window, aisle, exit row or front of the plane.