Southwest Airlines famously does not assign seats on its aircraft, and the carrier’s CEO recently vowed not to start doing so.

But the airline does charge fees for travellers who want to get onboard first and get the pick of the seats. And soon, that privilege will cost even more depending on what flight you’re on, USA Today reports.

The current flat $15 fee for EarlyBird Check-In, which affords travellers a priority spot on Southwest’s open-boarding line, will be replaced with a tiered fee system based on flight length and the popularity of early boarding on each flight.

Beginning August 29, 2018, EarlyBird Check-In will now cost $15, $20, or $25, depending on the flight.

EarlyBird Check-In cost a flat $10 when introduced in 2009, and has risen in price several times since. Southwest generated $358 million in revenues from the early boarding fee in 2017.

“We’re making this change so we can continue offering a product our customers love,” according to a statement from the airline. “Of course, an increase in the price of a product is rarely welcome news, but as EarlyBird increases in popularity, we want to protect the value it offers our customers.”