"Striking pilots must return to work by 6 pm today or face action," said the management.
"A strike needs a notice in advance. The Air India pilots have called in sick. Such kind of a strike is illegal," said Singh.
"This is not appropriate. Every section has grievances, they should have some patience," he said.
Atleast100 Air India pilots associated with the Indian Pilots Guild in Delhi and Mumbai failed to report for duty on Monday night citing health concerns.
Reports reveal that the number of pilots failing to turn up for work is expected to increase today.
The strike by the pilots is in a bid to show their protest against the decision to send domestic sector pilots for training on the Boeing 787 Dreamliner.
Four international flights have been affected by the strike. The cancelled flights include flights from Mumbai to New Jersey, New Delhi to Chicago, New Delhi to Hong Kong and New Delhi to Toronto.