(TNND) — United Airlines cut 35 round-trip flights a day from Newark Liberty International Airport, outside New York City, with the airline’s CEO blaming failed air traffic control technology and understaffing.

United CEO Scott Kirby said in a letter to customers late last week that “long-simmering FAA challenges boiled over” before he made the call to pull the flights.

Dozens of flights were diverted, and hundreds were delayed and canceled in recent days because of technology failures at the Newark airport, Kirby said.

“Unfortunately, the technology issues were compounded as over 20% of the FAA controllers for (Newark) walked off the job,” Kirby said. “Keep in mind, this particular air traffic control facility has been chronically understaffed for years and without these controllers, it’s now clear – and the FAA tells us – that Newark airport cannot handle the number of planes that are scheduled to operate there in the weeks and months ahead.”

Flight tracking company FlightAware showed Tuesday morning that the Newark airport had delays of nearly three hours.

Kirby said the company is canceling some Newark flights to minimize disruptions to its customers.

“It's disappointing to make further cuts to an already reduced schedule at Newark, but since there is no way to resolve the near-term structural FAA staffing issues, we feel like there is no other choice in order to protect our customers,” he said.

Last week, the U.S. Transportation Department announced new incentives to keep experienced air traffic controllers from retiring and steps the department said will speed up the hiring and training of new controllers.

Transportation Secretary Sean Duffy said the new "actions will supercharge the air traffic controller workforce from both retention and hiring side of the equation – bringing us one step closer to reversing decades of staffing declines."

The Federal Aviation Administration is on track to hire at least 2,000 controllers this year, the Transportation Department said.

The Transportation Department said the new incentives build upon steps already taken, including a 30% starting salary increase for academy trainees earlier this year.

Duffy also streamlined hiring by changing the old eight-step hiring process at the FAA to a five-step process, the department said. That move alone shaved months off the old hiring process, the department said.