Ed Miliband claims that if Labour gets in after the next election, they will freeze gas an electricity prices until the start of 2017.
Mr Miliband said: "The companies won't like it because it will cost them money. But they have been overcharging people for too long because the market doesn't work. It's time to reset the market."
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.