The airline was given 15 days to respond.

The regulator has also asked Kingfisher to stop selling tickets until its concerns are resolved.

“We are aware it is a big ask, but no potential investor will put his money in an airline that is not operational. Neither will our esteemed guests come back to us unless we commence operations soon,” Aggarwal wrote to staff.

Kingfisher, once India’s second-biggest airline, last week extended what it has described as partial lock-out until Oct. 12.

India recently allowed foreign airlines to buy a maximum 49% stake in local carriers, a move long lobbied for by Kingfisher, although no airline has publicly expressed an interest in investing in Kingfisher.

Mallya’s United Spirits Ltd and Diageo Plc recently confirmed long-rumoured talks for the U.K. giant to take a stake in India’s dominant whisky maker, which could make it easier for Mallya to find funds to rescue Kingfisher.

Since India’s investment policy change, “the dialogue with potential investors has gathered momentum,” Aggarwal said.

“Even non-strategic investors are showing interest in investing in Kingfisher Airlines, which is a good sign.”

Kingfisher has never made money since its launch in 2005, and before grounding its fleet last week, it was flying just 10 planes out of fleet that numbered 64 a year ago.