Kemi Badenoch has urged Andy Burnham not to cut energy bills for people on benefits this winter.
The Tory leader warned the Prime Minister not to 'launch an expensive energy bailout for Benefits Street' as the price paid by millions for electricity and gas rose again.
Her party said he was facing increasing pressure from the left to 'hand out more taxpayers' cash to households on welfare' to shield them against soaring bills.
It came after the price cap set by regulator Ofgem rose by 4 per cent on Thursday, taking the average dual fuel bill to £1,723.
Experts predicted it will soar by a further 16 per cent in January, taking bills to £1,999 as the conflict in the Middle East continues to hit gas supplies to the UK.
So far Mr Burnham has temporarily removed VAT from electricity bills, saving households about £45 a year in a move that came into force this week.
The Trades Union Congress is calling on him to go further and introduce a 'social tariff' that would cut bills by hundreds of pounds a year for those on the lowest incomes.
And some Labour MPs are said to be concerned that without fresh support, 'the vibes will end' for Mr Burnham's new Government.

Conservative Party leader Kemi Badenoch pictured after giving a speech last year
But Shadow Energy Secretary Andrew Bowie urged him not to provide more support to those on benefits.
He said: 'The siren call of the left for a Benefits Street bailout is growing louder by the day. But Britain cannot afford to blow even more taxpayers' cash on welfare.'
The Tories say every family would pay less for energy if ministers removed the Carbon Tax and renewables subsidies from bills.
They also want more drilling to be allowed in the North Sea, creating billions more in tax revenue, after Mr Burnham postponed a crucial decision on the Jackdaw and Rosebank sites for fear of losing votes to the Greens in next week's Holborn and St Pancras by-election.
Opposition leader Mrs Badenoch said: 'We need to return to common sense on energy. Britain should be drilling our own oil and gas in the North Sea and using the tax revenues to bring down bills. We should also scrap all the Net Zero levies and subsidies that force up the cost of energy bills.
'Instead, Andy Burnham is tinkering around the edges, and even backtracking on his promise to drill our own oil and gas because he's scared about the Green Party winning a by-election in London. None of this is doing anything to help people facing rising bills this winter.'
A Labour Party spokesman said: 'Andy Burnham's core focus is easing the pressure on the cost of living. Over the summer one of his first acts as Prime Minister was to cut taxes on energy bills.
'Nobody needs lectures from a Tory Party who crashed the economy and let the benefits bill soar. While they snipe from the sidelines, Labour will get on with bearing down on the cost of living and driving good growth in every postcode of Britain.'
In a round of regional BBC interviews ahead of her party conference in Birmingham, Mrs Badenoch said Mr Burnham's speech to Labour this week suggested he will call an early election despite his insistence that he will not.
'All the policies he announced are for after an election, so if he's not calling an election why is he talking about things happening in 2030?
'He says a lot of things with a smile, but I actually think that he's got very different plans for us and for our country,' she said.