Energy provider PrepayPower has said that it will increase it gas and electricity prices from 1 October.
Electricity prices are to rise by 19%, while gas prices will increase by 29%.
The increases will add an additional €339 to the average electricity bill and €428 to the average gas bill.
The company, which has 170,000 electricity customers and 60,000 gas customers, said that the increases are as a result of "continued upward price pressure on international energy markets".
A spokesperson for the company said: "Regrettably, surging international wholesale costs make customer price increases inevitable.
"Were it not for our extensive hedging operations, these increases would have had to be significantly higher.
"We continue to work hard to protect customers to the greatest extent possible from the impact of these international developments."
This morning, Minister for the Environment Eamon Ryan said that large energy bills are unavoidable for households this winter and Government will have to address this with financial supports and advice.
He said that everything would be done to avoid blackouts but there are no absolute guarantees.
The minister also confirmed that Government will look at storing backup gas supplies to deal with the energy shortage. A range of options to achieve this would be presented to Government later this week and this would be followed with a public consultation.