United Airlines will pause pilot hiring this spring because of aircraft deliveries from Boeing, the latest effect of the plane maker’s problems with one of its biggest customers.

New hire classes will be paused in May and June and will likely resume in July, Marc Champion, vice president of flight operations, and Kirk Limacher, vice president of flight ops planning and development, told staff Thursday in a memo, which was seen by CNBC.

“We wanted to let you know that United will slow the pace of pilot hires this year due to continued new aircraft certification and manufacturing delays at Boeing,” they wrote.

Boeing didn’t immediately comment.

Boeing has been struggling with a host of production flaws like incorrectly drilled holes on the fuselage and the fallout from a door plug that blew out of a nearly new Boeing Max 9 operated by Alaska Airlines on Jan. 5, which prompted a brief grounding of the aircraft type earlier this winter. Bolts appeared to be missing on the plane when it left Boeing’s factory, a preliminary investigation found.

United was contracted to receive 43 Boeing 737 Max 8 and 34 Max 9 models this year, but expects to get 37 and 19 of them, respectively, according to a company filing. It also had contracted deliveries of 80 Max 10s in 2024, the largest model in the bestselling Max family, but expects none of them this year. The plane hasn’t yet been certified yet by the Federal Aviation Administration and is years behind schedule.

United’s CEO, Scott Kirby, in January said the carrier is making a fleet plan without the Max 10.

“As you know, United has hundreds of new planes on order and while we remain on a path to be the fastest growing airline in the industry, we just won’t grow as fast as we thought we would in 2024 due to continued delays at Boeing,” Champion and Limacher said Thursday. “For example, we had contractual deliveries for 80 MAX 10s this year alone – but those aircraft aren’t even certified yet and it’s impossible to know when they will arrive.”

Other U.S. carriers have slowed pilot growth this year following a hiring spree in the past few years, after encouraging staff to take early retirement when demand slumped in the pandemic.

A shortage of aviators along with slow aircraft deliveries from both Boeing and Airbus as they faced supply chain constraints have helped drive up airfares.

American Airlines hired about 2,000 pilots last year and expects to add around 1,300 this year, CEO Robert Isom said at an investor presentation in New York on Monday.

“That’s slowing down a little bit, but … we have a considerable number of retirements,” he said. “We will be hiring for the foreseeable future at levels like that.”

Delta Air Lines is halving its pilot hiring this year after bringing on a record 2,400 in 2023, and Southwest Airlines will pause pilot hiring after a new-hire class this month, a spokesman said. Some carriers like Spirit Airlines have stopped pilot hiring altogether to slow their growth and reduce costs.