Budget carrier Jetstar Japan canceled two domestic flights on Sunday covering a round-trip service between Narita and Fukuoka airports, as it could not secure the crew needed for operation, an airline official said.

This is the first time that Jetstar's flights have been canceled due to a crew shortage, with some members of the company's flight crew labor union on strike since Friday. But the official denied that the strike had caused the disruption and instead cited illness as the reason for the cancellation.

According to the union, several pilots and flight attendants have been on strike each day, with around 120 members refusing unscheduled work on holidays from early December.

The airline often asks crew members who are on holiday to stand in for colleagues who are unable to turn up for work due to illness.

The union launched the strike following a breakdown of negotiations with management over employees' unpaid wages; the union claimed that the company had calculated overtime work erroneously.

The union plans to continue the strike through Jan. 7.