Household gas bills are set to soar by more than 20% in the autumn.
Bord Gais asked the energy regulator if it could hike its prices by 28% because of the steep rise in buying fuel in from international wholesale suppliers.
But the regulator said it would not allow any more than a 22% jump.
The increase is expected to add around €150 to the average home gas bill.
The Commission for Energy Regulation (CER) is to officially approve the increase next month.
It will come into force at the beginning of October.
Earlier this month, Bord Gais announced that its electricity bills will jump by 12% from August 1.
Average electricity prices with Bord Gais currently stand at €989 a year, with gas at €689.
The company is already working with 110,000 customers who are behind with their payments.