Southwest Airlines shares fell roughly 4% in premarket trading Wednesday after the carrier cut its second-quarter revenue forecast, citing changing booking patterns.

Southwest expects revenue per available seat mile, the amount the airline brings in for every seat it flies one mile, will fall between 4% and 4.5% in the second quarter over last year, after previously estimating a 1.5% to 3.5% decline.

It also said its unit expenses, excluding fuel, would be up as much as 7.5% over the year-earlier period, after previously expecting no change.

It said its capacity would rise as much as 9% instead of the flat growth it had previously expected in how much it flies.

Southwest still expects record quarterly operating revenue in the second quarter.

Airlines are raking in record numbers of passengers but higher costs and growth in capacity have weighed on fares and profits.

“The reduction in the Company’s RASM [revenue per available seat mile] expectations was driven primarily by complexities in adapting its revenue management to current booking patterns in this dynamic environment,” Southwest said in a filing.

Other carriers like Delta and United, meanwhile, have been enjoying passengers’ return to international travel and have invested heavily in travelers’ willingness to pay more for roomier seats.

Southwest is under activist investor pressure from hedge fund Elliott Management, which has called for CEO Bob Jordan and Chairman Gary Kelly to be replaced, saying the company is underperforming and needs a change at the top.

The Dallas airline has expressed confidence in its leadership and reiterated that it is considering revenue initiatives like seating assignments or premium seating, which would be massive changes to the company’s simple business model that has been profitable for most of the last five decades.

“We will adapt as our customers’ needs adapt,” Jordan said at an industry event hosted by Politico earlier this month.