British Gas owner Centrica is seeking a judicial review against Ofgem over how the regulator calculated wholesale costs when it set the level of the incoming energy price cap.
The energy company has insisted it does not intend to delay the implementation of the cap, which is due to come into effect on 1 January 2019.
Centrica has previously made no secret that it does not believe the measure will “benefit customers”.
Ofgem said it will defend its proposals “robustly”.
Centrica announced last month that it expects its profits to be reduced by £70 million in the first quarter of 2019 due to the introduction of the price cap on default tariffs.
The firm’s trading update also revealed it lost 372,000 domestic energy supply accounts in the four months to the end of October after it increased its prices by 3.8 per cent in the summer – its second price hike of the year.
Centrica has stressed that it does not believe Ofgem has calculated the price cap fairly.
In a statement about its decision to seek the judicial review, the parent company of British Gas – the largest energy supplier in the UK, said: “Centrica plc is seeking judicial review of Ofgem’s decision of 6 November 2018, which relates only to the treatment of wholesale cost transitional arrangements and Ofgem’s decision not to investigate and correct its failure to enable the recovery of the wholesale energy costs that all suppliers incur.
“Through this action Centrica has no intention to delay implementation of the cap and does not expect the cap to be deferred in any way.
“As we have previously said, we do not believe that a price cap will benefit customers but we want to ensure that there is a transparent and rigorous regulatory process to deliver a price cap that allows suppliers, as a minimum, to continue to operate to meet the requirements of all customers.”
A spokesperson from the regulator added: “Ofgem carried out an extensive consultation process when setting the price cap and we believe that it offers consumers on poor value tariffs a fairer deal.
“In the event of a judicial review we would defend our proposals robustly.”
On 6 November, Ofgem set the final level of the incoming energy price cap at £1,137, just £1 higher than the proposed amount.
The cap was subject to the statutory consultation process after the £1,136 price was first revealed on 6 September.
According to Ofgem, 11 million households on poor value default tariffs are set to save around £76 on average, while a typical consumer on the most expensive tariffs would save more than £120.
The regulator has already indicated that if the trend of rising wholesale costs continues it is likely that in February it will announce an increase for the price cap for April 2019.