British Gas, EDF, RWE npower, SSE, E.ON and ScottishPower have all been summoned to appear before the Energy and Climate Change Select Committee to account for their pricing polices.
Here is a breakdown of the energy firms, known as the "Big Six":
The company is increasing electricity bills by 10.4 per cent and gas tariffs by 8.4 per cent for around 7.8 million families this winter.
The Centrica-owned energy giant said average customer dual-fuel bills will rise by £123 to £1,444 a year according to Ofgem usage figures after the price increases, which take effect on November 23.
The move sees British Gas tear up a pledge made earlier this year to use an annual earnings windfall from the cold weather to keep a lid on tariffs.
It is being represented by managing director of energy Ian Peters at the select committee.
The firm is yet to announce an increase in prices.
Last year they rose by 10.8 per cent to £1,251 a year, when it was also one of the last to declare it.
EDF is sending Martin Lawrence, its managing director of energy sourcing and customer supply to the committee.
RWE npower will put up electricity and gas prices by 9.3 per cent and 11.1 per cent respectively from December 1.
The 10 per cent average bill increase will affect about 3.1 million customers.
The price hike will mean an average dual fuel customer's bill rises by £137 a year, from £1,323 to £1,459.
RWE npower also raised tariffs by 8.9 per cent last November.
The company will be represented by external affairs director Guy Johnson at the select committee.
SSE was the first of the major energy companies to announce it was raising gas and electricity bills. Its increase of up to 10 per cent will add a typical £106 to annual dual-fuel customer charges to reach £1,380.
The company said wholesale energy prices were up 4 per cent, paying to use newly-upgraded networks by 10 per cent and Government-imposed levies up 13 per cent.
SSE is sending its managing director William Morris to the committee.
The company, formerly known as Powergen, has not yet announced price rises this year.
It is the only one of the companies whose chief executive, Tony Cocker, will represent it at the committee.
The group said it will raise gas tariffs by 8.5 per cent and electricity prices by 9 per cent on average from December 6, adding another £113 to the typical annual dual-fuel bill.
Spanish parent firm Iberdrola warned in third-quarter results last week that it had "no option" but to increase tariffs in the UK after claiming ScottishPower had been hit by the Government's energy-efficiency and environmental measures.
The company is sending its chief executive of retail and generation Neil Clitheroe to the select committee.Reuse content