Energy firm Npower is to cut up to 2,500 jobs, more than a fifth of its UK workforce, with details to be announced this week.
Npower, which is owned by the German energy giant RWE, employs 11,500 people in Britain and is one of the big six gas and electricity suppliers in the UK.
The company has declined to comment on the news.
Last year it posted a loss of £48m for the first nine months of the year.
In February Npower announced a 5.2% cut in its gas price, taking effect on 28 March – a £32 average annual reduction to customers on a standard domestic tariff.
Like other energy suppliers, it is under pressure from ministers and consumer groups to lower energy bills for customers amid a rapid decline in oil prices.
The news on job losses also comes days before UK competition regulators unveil plans to make the energy market more transparent for consumers.