Firmus Energy is putting up gas prices for its 85,000 customers in Northern Ireland.
The provider said it would add £39 to the average annual domestic bill and the change will take effect next month.
Firmus Energy said the move was “regrettable”, but said this reflected its own increased costs.
“The cost of bringing natural gas to our customers has increased and our price rise has been unavoidable,” said Michael Scott, its managing director.
Around 50,000 of Firmus Energy’s customers are in greater Belfast and their bills will increase by 8.8% from 16 April.
Its remaining customers, in what is known as the Ten Towns area, face a 6.8% hike from 5 April.
This covers Londonderry, Ballymena, Armagh and Newry, among other places.
Last week, another supplier, SSE Airtricity, announced it was increasing prices by 7.7% for its 150,000 customers.
Kevin Shiels, the Utility Regulator’s director of retail and consumer protection, said: “We understand price rises are not welcome.
“Following these increases, we would encourage consumers to shop around to make sure they are getting the best deal for their gas supply.”