The stock tumbled 6.13 per cent to Rs 1,161.05 on the BSE. On the NSE, it went down 6.22 per cent to Rs 1,160.05.
The stock had fallen over 2 per cent in the previous session also.
The letter from IndiGo President Aditya Ghosh to this effect was sent to Minister of Civil Aviation Gajapathi Raju soon after the Cabinet on Wednesday gave its in-principle approval to Air India's disinvestment.
IndiGo is the market leader in the domestic aviation sector with a share of little over 41 per cent.
Air India has a debt of Rs 52,000 crore and is surviving on a bailout package of Rs 30,000 crore approved in 2012.