"Yesterday and today 40 cabin crew members, or 25 per cent of the staff, took sick leave, which has never happened in Croatia Airlines before," Kucko told a press conference at Zagreb Airport.

Kucko said that the company had requested a formal investigation of the causes of sick leave and of doctors who had authorised the sick leave requests. He said he was surprised that this was happening at a time when the national carrier was recording excellent business results.

"The first quarter of the year was the best in the company's history as we got rid of the debts and are now expecting a successful season," Kucko said.

When asked why he suspected the sick leave requests were unjustified, Kucko said that three of the six unions active in the company had signed the new collective agreement while the remaining three had not.

"We have reason to believe that this is a kind of work to rule and protest by the cabin crew union as a result of their disagreement with the proposed collective agreement," he said, confirming that the management board intended to reduce the number of days off with a view to increasing productivity and could no longer guarantee 15 days' annual leave because of the company's seasonal nature. He called on the trade unions that had not signed the collective agreement to continue negotiations with the management.

Kucko said that 10 international and three domestic flights had been cancelled and that about 350 passengers had been referred to Croatia Airlines' partner, Star Alliance. He said that the damage done was not great because the passengers were able to continue their journey within three hours, but that the lease of the aircraft was a considerable cost to the company.