Around half of the money generated from energy price rises over past two years has gone into the profits of the "Big Six" firms, Ed Miliband will say today.
The scale of the problem is so bad that householders need a price freeze now, not in 18 months as his party had originally planned, the Labour leader will warn.
He will also announce plans to force a vote in the Commons on the issue tomorrow.
But an energy price freeze is unlikely to find the support of the majority of MPs.
The idea from Labour has already been denounced as a "con" by both the Conservative and the Liberal Democrats.
Mr Miliband is expected to set out new figures showing how the wholesale cost of energy has risen at an average rate of 1.6% a year since 2011, while the Big Six energy companies have increased retail prices by an average of 10.4% a year.
As a result, he will say, more than half of the rise in people's bills has gone straight back to those Big Six firms.
In a speech he will give in London on living standards, Mr Miliband will say: "For the next 18 months, people will hear scare stories from the unholy alliance of the energy companies and David Cameron: the Big Seven.
"It will just reinforce in people's minds who he stands up for - the six large energy companies, not the 60 million people of Britain."
Mr Miliband will also insist that a price freeze is "workable".
"And tomorrow, Conservative and Liberal Democrat MPs could vote for it," he will say.
He will add: "If they line up against it, the British people will know the truth: this government is on the side of the big energy companies, not hard-pressed families."
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