Rishi Sunak must cancel April's planned cut in the energy support scheme with bills at sky-high levels, Labour's Rachel Reeves is set to demand.
The Shadow Chancellor will urge the Prime Minister to pass on a recent fall in wholesale gas prices to struggling households.
In a speech on Saturday she will accuse Mr Sunak of "burying his head in the sand" as the cost-of-living crisis bites.
Ms Reeves will also outline Labour's plan to slash households bills by £1,400 per year by the end of the decade if the party wins power.
Under the Government's "energy price guarantee" typical bills are frozen at an average of £2,500 - but will soon become less generous.
Six savings challenges to take in 2023 - how you could save thousandsIn November the Chancellor Jeremy Hunt announced the cap will be increased to £3,000 for the average household in April.
There are also no plans by the Government to extend a£400 payment made available to all households across the country this winter.
Speaking at the Fabian's annual conference, Ms Reeves say: "Millions of families are still looking to a 40% increase in their energy bills, in April.
"On a week when temperatures fall below zero, I know many families and pensioners will be feeling the pressure particularly acutely.
"At the same time, energy companies continue to enjoy record profits. This cannot be right."
The senior Labour MP will claim that keeping the energy price guarantee at the existing level could be paid for by extending a tax on the excess profits of oil and gas giants.
She will add: “That those who have profited from the windfalls of war should shoulder their share of the cost, so ordinary people do not have to bear the brunt of a crisis that they did not cause.
“By backdating this from the start of 2022 - when oil and gas giants were already making historically large profits - we can raise more than £13bn."
Under plans to save households hundreds of pounds off energy bills, Ms Reeves will also commit to reaching "100% clean power by 2030 and retofit millions of homes" by 2030.
“Sticking plaster politics is not enough," Ms Reeves will say.
I'm a heating expert - eight tips to save up to £1,900 on your bills this year“We cannot persist with walking into a crisis unprepared, and at the last minute producing hugely expensive fixes to get us through, while the underlying problems – those weakened foundations – remain untouched."