Energy regulators should limit the amount of money energy suppliers can back-bill consumers when they charge them incorrectly, according to the Energy Advice Line.
Julian Morgan, managing director of the price comparison, switching and advice service for energy users, said householders and businesses should not have to suffer unexpected demands for money due to billing errors that were not their fault.
Last month it was revealed that millions of households had faced back bills averaging £206 after suppliers initially undercharged them in error. One in six people were told they were owed more than £250, while some people were hit with four-figure sums out of the blue.
Citizens Advice, which revealed the back billing problem, said 16,000 people had contacted the charity last year with bill concerns, and were worried about how they were going to pay.
"It's not fair that suppliers can back bill customers out of the blue for up to 12 months worth of gas or electricity, when they themselves were in error, due to a technical problem for example," Mr Morgan said.
"This places an unforseen burden on the budgets of households, as well as businesses, which I know suffer from this problem too.
"Customers should not have to pay the price for suppliers' mistakes. Consumers are already struggling with skyrocketing energy bills and this is the final straw for many who find it difficuly to make ends meet.
"Ofgem should drastically reduce and cap the amount of money suppliers can back bill customers.
"It should also ensure that consumers have a reasonable length of time to pay these belated bills.
"There is little incentive for suppliers to issue accurate bills when they can demand payment retrospectively. This is unfair and needs to change."
The Energy Advice Line is one of the UK's leading price comparison and switching services for business and domestic energy customers. It is also an advocate for energy market reform and has campaigned for a better deal for energy users, including calling for a ban on cold calling and changes to regulations to make it easier for all consumers to switch suppliers.
The service is completely independent and free. Consumers can quickly and simply search the market for the best available energy deals from an extensive panel of small and large energy suppliers. The service also offers a free advice line for business energy customers.
For further information visit energyadviceline.org.uk