Shadow energy secretary Caroline Flint said firms "must come clean" about why they have chosen to raise energy prices "when they are already making huge profits".
Speaking ahead of the appearance of directors from the "Big Six" companies before MPs, Ms Flint said: "The latest revelations about rising profits and the growing gap between wholesale costs and household energy bills highlight why answers are needed.
"Britain's energy market isn't working for ordinary families and businesses."
The so-called big six energy companies were forced to explain to Parliament why bills are increasing so much this winter.
As the 'Big Six' energy firms prepare to face MPs over rising prices, here are a few facts on what makes up your energy bill.
The UK spends below average per kilowatt of energy in comparison to other EU countries.