A cyberattack targeting a service provider for check-in and boarding systems has caused disruptions at several major European airports, such as London’s Heathrow, Brussels, and Berlin, leading to flight delays and cancellations on Saturday.

According to London’s Heathrow Airport, Collins Aerospace, which supplies check-in and boarding systems to several airlines across numerous global airports, is facing a technical issue that may result in delays for departing passengers. The airport warned about potential delays on Saturday.

RTX Corporation, Collins Aerospace’s parent, was not immediately available for comment outside of US business hours.

The attack has rendered automated systems inoperable, allowing only manual check-in and boarding procedures, Brussels Airport said on its website.

“This significantly impacts the flight schedule and will unfortunately lead to delays and cancellations of flights… The service provider is actively addressing the issue and striving to resolve the problem as swiftly as possible.”

Passengers with a flight scheduled for Saturday were advised by the affected airports to confirm their travel with airlines before heading to the airport.

“Due to a technical issue at a system provider operating across Europe, there are longer waiting times at check-in. We are working on a quick solution,” Berlin Airport said in a banner on its website.

Frankfurt Airport, Germany’s largest, was not affected, a spokesperson said.

An official from the operations control center at Zurich Airport also said it had not been impacted.