Conservative Party chairman Grant Shapps said a price freeze would actually increase household energy bills over the next two decades.
"While we're forcing energy companies to put their customers on their cheapest tariffs, Ed Miliband would introduce an energy policy that would add £125 to the typical household's bill," he said.
The party said a 2030 decarbonisation target supported by Labour would mean a rise of that scale over the next 17 years.
As Ed Miliband clashes with the energy giants on prices, it is worth knowing how your expensive energy bills are actually made up.
A leading competition lawyer says an energy price freeze could leave Labour open to challenges from the courts or the European Commission.
Whether or not you approve of a state intervention into industry, there are at least two big potential obstacles for an energy price freeze.