The government owned gas utility firm had approached the Delhi high court over the constitutionality and legality of the powers of PNGRB to fix network tariffs.
In April, the regulator (PNGRB) had ordered IGL to cut network tariff by around 60 per cent retrospectively from April 2008. The total refund on account of the retrospective nature of the order was pegged between Rs 900-1,200 crore.
IGL had argued that the order would wipe out the company's entire net worth of Rs 1,500 crore.
The court said that the PNGRB does not have the power to fix network tariff or the power to decide any component of the retail price.
Shares in IGL had plunged 33.7 per cent to end at Rs 229.80 on 10 April when the order was made public. Since then the stock had failed to recover.