Turkish Airlines employees went on strike on Wednesday in a dispute over pay and the reinstatement of sacked workers, but the company said its operations were continuing as planned with planes leaving on time.
Aviation union Hava-Is, which represents 14,000 of the airline's 15,800 workers, is demanding the company rehire 305 staff dismissed after industrial action that grounded hundreds of flights in May last year.
"Our strike began at 3am and is continuing," the union said on its website.
There was a heavy police presence at Istanbul's Ataturk Airport, where members of Hava-Is gathered to hold a protest, while the airline issued a statement indicating no disruption to its services.
Members of the union, mainly those who were fired last May, have held a vigil outside the foreign arrivals terminal at Ataturk since the dismissals last year.
"All our employees stood up for their company and disregarded the strike," the company said in a statement.
"Turkish Airlines is continuing its daily operations as planned with flights happening on time," it added.
However, a union official said disruption would begin in the hours ahead.
"Most of the flights so far have been on time, but they have started to call colleagues who are joining the strike ... Flights will begin to be delayed within a few hours," a union official told Reuters.