(Bloomberg) -- Airlines serving Amsterdam Schiphol airport said the hub’s move to cut capacity amid staffing shortages has seen it pressure them to switch to smaller planes or leave seats empty.

Air Serbia has been asked to reduce occupancy levels by about 28% on flights to Belgrade from July 7, it said in an email. Latvia’s AirBaltic Corp AS said Tuesday it has also been asked to curb passenger loads on outbound services from the Dutch base.

Schiphol, one of western Europe’s four main hubs prior to the coronavirus pandemic, has been among the airports hardest hit by shortages of security staff and other workers as travel demand rapidly rebounds. It last month capped summer passenger numbers almost 20% below usual levels to avoid the chaos of last-minute delays and cancellations, leading to the mass elimination of flights from schedules at carriers including KLM and EasyJet Plc.

Air Serbia said that it had written to Schiphol asking it to reconsider the requirements for reducing seating. It and AirBaltic both said that they’re considering legal action to seek compensation from the airport operator.

The Serbian firm, which operates nine weekly flights from Amsterdam, said the restrictions would cause it “great financial and reputational damage” due to the number of booked passengers who couldn’t be re-accommodated.

A spokesperson for Schiphol said the airport is asking various airlines to reduce capacity in line with the passenger cap for July and August aimed at avoiding “unmanageable queues.”

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