Energy bills across the UK are set to rise in April, with four million households having to find an extra £81 a year - according to reports.
Experts say the regulator Ofgem will unveil an £81-a-year raise in the price cap for pre-payment energy meters.
Those on standard tariffs - 11 million households - could face a £66 a year raise in the cap.
Meters tend to be used by people who could otherwise struggle to pay their bills, reports The Mirror.
Robert Buckley, of energy consultants Cornwall Insight, said rises are driven by higher wholesale energy costs which, unless they fall, may see the cap rise again by another £40 or £50 next winter.
Adam Scorer, of the charity National Energy Action, said other customers can avoid higher bills by switching supplier or tariffs.
But he said: “PPMs users are often trapped, with no options and just have to take the hit or keep the heating and power off.
"This will hit millions of pre-payment customers who are already facing a tough winter. They should be better protected from price rises.”
Cornwall believes Ofgem will raise the cap by £66 for 11 million customers on standard tariffs, who also face a £21 a year charge to cover others missing repayments due to the Covid-19 crisis.
Ofgem declined to comment.
