A new campaign has been launched to improve tariffs for customers with prepayment meters (PPMs).
The National Housing Federation has decided to act after figures revealed that customers using the system can be charged £100 more than people who receive their energy bills quarterly.
Commenting on the findings with the Guardian, Labour MP for Southampton Test Alan Whitehead said that major energy suppliers were being "unfair" to those on lower incomes who use PPM systems.
He commented: "Energy companies are using unfair tariffs on prepayment meters to rip off their most loyal customers and some of the poorest people in society. The government and Ofgem should take action now."
The NHF hopes that its campaign will lead energy suppliers to bring their PPM tariffs in line with their quarterly billed costs.
New pressure on the UK's major energy companies has come after the European Union announced plans to "unbundle" the continent's major gas and electricity suppliers to create more competition in its member states' energy markets.
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