Four Air India international flights were cancelled on Tuesday after about 100 pilots called in sick, evoking a strong response from the airline management which asked them to return to work by 6 PM this evening or face action.

Civil aviation minister Ajit Singh termed the strike as "illegal" and said the management of the national carrier would take appropriate action against those involved in the stir.

"The pilots have been told to return to work by today evening. And if they don't, the management will take stern action against them," Air India spokesperson said.

A section of Air India pilots owing allegiance to Indian Pilots Guild are agitating over the rescheduling of Boeing 787 Dreamliner training. Four AI international flights were cancelled from Delhi and Mumbai after about 100 pilots refused to join work.

It is understood that the management has also decided to send doctors' team to the pilots' houses, who are reporting sick, to protest against the rescheduling of Boeing 878 Dreamliner training.

"We have decided to send doctors' team at the residence of the pilots, who are reporting sick. It is our primary duty to enquire about their health," airline sources told PTI.

Meanwhile, the Nationalist Congress Party (NCP)-backed pilots' body has said that it is open to negotiations with the management.

"We are open to negotiations at any given time," Indian Pilots Guild president and NCP leader Jitendra Awhad told PTI.

The Civil Aviation Minister said the pilots went on sick leave in the midst of their talks with the management of Air India which has led to cancellation of flights.

"They are reporting sick. They have not given any notice for any strike. So whatever the Air India management rules and regulations, action will be taken accordingly," Singh told reporters here.

Noting that Air India is currently undergoing a turbulent period and crores of public money is being infused to run the carrier, Singh said every section has grievances and that there are ways to find a solution.

"Strike is illegal. There is a way to launch a strike. Every section has grievances and problems. But there are ways," he said.