Staff at Zagreb airport, which is to be taken over by a French consortium, will go on a two-day strike Thursday during which all commercial flights will be cancelled, unions said.
The strike will start at 0900 GMT on Thursday and end at 2300 GMT on Friday, state-run HINA news agency on Wednesday quoted the airport unions as saying.
Commercial flights will be redirected to other airports while only emergency medical, army and government flights will be allowed at Zagreb Pleso airport, the unions said.
Unions fear that employees may lose their benefits and jobs in the long run once the airport is taken over by the ZAIC consortium led by Aeroports de Paris (ADP).
However, airport CEO Miroslav Drljaca said the strike was "unfounded and illegal" as employees were enjoying better rights than most Croatian workers. They would also keep both their benefits and jobs for at least five years, HINA reported.
Some 60 flights will be cancelled and direct damages should amount to some 900,000 kuna (118,000 euros, $158,000) a day, Drljaca said.
In 2012, the government and ZAIC signed a deal for a 30-year concession to manage Zagreb Pleso airport and construct a new passenger terminal, an investment estimated at more than 230 million euros.
The new terminal will have an annual capacity of five million passengers. Currently Zagreb airport can process around two million passengers a year.