Liberal Democrat Energy Secretary Ed Davey warned that a price freeze could result in the lights going out.
"Everyone wants to help with the cost of rising bills, which is why Liberal Democrats have cut income tax by £700 for working people. But Labour's plan is a promise that won't work," he said.
"When they tried to fix prices in California it resulted in an electricity crisis and widespread blackouts. We can't risk the lights going out here too.
"Fixing prices in this way risks blackouts, jeopardises jobs and puts investment in clean, green technology in doubt."
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.