Bord Gáis wrote off €26.4m in bad debts last year as a result of customer arrears.
The company estimates that around 115,000 households are now in arrears for more than 60 days.
According to its annual report, the company recorded pre-tax profits of €120m.
Bord Gáis now has around one million customers, among them 460,000 electricity customers.
CEO of Bord Gáis John Mullins said that bills were always higher for the first few months of the year, due to the cold weather, and that this pattern was particularly marked this year, especially in December.
He added that, on top of the severe winter, "we have to accept there are real issues in the economy" which are putting additional pressure on people.