BRUSSELS — Amsterdam’s busy Schiphol Airport is warning passengers about likely delays due to a nationwide public transport strike.

Most Dutch buses, trains, trams and ferries lay idle Tuesday as unions held a one-day strike as part of a campaign against rising retirement ages.

Schiphol spokeswoman Madelon van der Hof said about 80 flights were cancelled at the airport. National carrier KLM offered passengers the option of changing their bookings free of charge to avoid the strike.

Only four trains per hour were operating between the airport and Amsterdam instead of the usual 25. The airport says on its website: “Do not travel to Schiphol unless strictly necessary.”

Schipol’s website (schipol.nl) also says: “The Dutch labour union FNV has called staff of security, cleaning, baggage, apron and check-in to strike today (Wednesday 29 May). This may have consequences for your journey. Are you flying from or to Schiphol today? Please take account for longer waiting times because of the strike. It might be possible that your flight will depart later. Of course, we will do everything we can to limit disruptions. We apologize in advance for any inconvenience.”

Amsterdam authorities have opened a major tunnel under the Ij waterway to bicycles so that commuters can pedal to work.