Dutch airline KLM is cancelling up to 50 flights a day during this upcoming long weekend due to overcrowding at Amsterdam Schiphol airport, it said on Friday.

This will include Friday and Monday, a national holiday in the Netherlands.

Passengers on the affected flights are rebooked on other flights, the Dutch arm of airline group Air France-KLM added.

“KLM has also freed up seats on certain flights, so that passengers who do not make their flight or transfer due to crowds at the airport, can still depart at a later time in the day,” the airline said in its statement.

Schiphol airport, Europe’s third-busiest airport, has been grappling with overcrowding due to a shortage of security staff. Earlier this week the airport agreed to increase the wages of staff over the summer period and to hire more personnel.

In an effort to avoid overcrowding, Schiphol has asked passengers to arrive not more than four hours in advance.