(Bloomberg) -- London Gatwick Airport will temporarily limit capacity to 800 daily flights after a rising number of sick leaves at the traffic-control unit disrupted operations, 

The cap, which took effect on Monday and runs through Oct. 1, responds to the fact that 30% of tower staff at the NATS air traffic control unit are currently unavailable for different medical reasons, including Covid, according to the company. Gatwick first suffered major disruptions over the weekend amid mounting sick leaves.

Ryanair Holdings Plc said airlines being asked to cancel flights to and from Gatwick because of the staffing shortage was unacceptable. The Irish low-cost carrier said it refused to scrap any of its Gatwick flights and instead called on NATS Chief Executive Officer Martin Rolfe to resign.

“This has been a difficult decision but the action we have taken today means our airlines can fly reliable flight programs, which gives passengers more certainty that they will not face last minute cancellations,” Stewart Wingate, the head of London Gatwick, said in a statement.

The cancellations threaten to disrupt travel for as many as 25,000 travelers, based on calculations of axed flights. While Gatwick provided no exact figure, it said the estimate is “broadly accurate.”

The reduction to 800 movements compares with as many as 865 flights per day that were set to take place this week. London Gatwick is the second major airport in the south of the UK, alongside Heathrow, and the hub is an important airfield for discount carrier EasyJet Plc.

Johan Lundgren, the EasyJet chief executive officer, called the move “regrettable” but one that is beyond the airline’s control.

The flight limit is specific to Gatwick, NATS said in a separate email. Heathrow said it’s not affected and doesn’t plan to introduce any caps to flights. NATS expects operations to improve gradually as staff return to work and summer travel slows down, it said.

Manchester Airport, located about 200 miles (320 kilometers) north of London, said it may end up receiving some flights that were destined for Gatwick, given the airport’s size and the fact that it has multiple terminals, the operator said. 

--With assistance from Charlotte Ryan.

(Updates with estimate on possible disruption in fifth paragraph.)

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