More than 120,000 natural gas customers in Belfast are facing a hike of almost 9% in their bills.
Airtricity has blamed the 8.7% rise in its prices on a number of factors, including cost increases it said were outside of its control, such as transmission and distribution rates.
The supplier said the change was the equivalent to an increase of under £1 per week or 13p per day on a typical domestic gas bill.
Airtricity's gas network in Northern Ireland extends across the Greater Belfast area. Around 115,000 domestic and around 6,500 small business customers will be affected by the price rise. The company said the cost of its electricity prices would not be impacted by the gas bill increase.
Northern Ireland's Utility Regulator has approved the move.
Stephen Wheeler, Airtricity's managing director, said: "Increasing prices is one of the hardest decisions any energy provider has to take and we deeply regret having to do so. Last year we were able to reduce and then hold our gas prices; however, in recent months we have seen significant increases in costs outside of our control. These increases are external to our business and include a rise in the cost of using the gas transmission and distribution network to carry gas to our customers as well as a tariff adjustment, approved by the Utility Regulator, to correctly recover our gas supply costs over time. As a result we have no choice but to increase our prices at this point."
Mr Wheeler said his company had consulted with the Consumer Council and the Department of Enterprise, Trade and Investment ahead of making the increase, which will come into effect in April. "As ever, we will continue to do everything to ensure we deliver value to our customers in their energy supply, the greatest possible help and the very best service that our customers have come to expect from us," he added.
Chief executive of the Utility Regulator Shane Lynch said he recognised the increase would hit consumers.
"Although this is the first gas price increase for two years, we recognise the impact that it will have on consumers at a time when household and business budgets are stretched. We never approve proposals for tariff increases without extensive scrutiny. Our scrutiny during this tariff review has reduced the extent of the increase sought by Airtricity. If gas costs decrease, we will act as soon as possible to ensure that this reduction is reflected in consumer bills."
He added: "The tariff increase will still leave the standard domestic average tariff for Greater Belfast gas consumers lower than their equivalents in Great Britain or the Republic of Ireland. It is also important to note that consumers who choose natural gas enjoy significant running cost savings over those who use oil to heat their homes."