After doing so to Kingfisher Airlines, the Directorate General of Civil Aviation has issued showcause notices to carriers IndiGo and SpiceJet for having allegedly cancelled flights without informing passengers.
"We have information that both had not operated 30 flights each daily, without information," said E K Bharat Bhusan, the director-general.
The aviation regulator clears two schedules, winter and summer. The winter schedule starts from October and ends in March every year.
IndiGo president Aditya Ghosh said they'd replied to the notice.
"IndiGo has not cancelled a single flight. The approved winter schedule is for the flights to be operated up to March 2012. IndiGo operates 259 domestic flights daily. As we induct seven more aircraft into our fleet from now to March 2012, we will add flights to fulfil all our winter schedule approvals," he said.
SpiceJet's chief executive officer, Neil Mills, did not reply to SMSes and phone calls.
IndiGo is the third largest carrier on passengers carried, with an 18.7 per cent market share in August, a notch below the 18.8 per cent of Kingfisher.
SpiceJet is the fifth largest, with 13.4 per cent of all passengers in August.