E.ON has become the fourth of the 'Big Six' energy providers to announce price rises this summer.
Customers will have to pay 11.4% more for their electricity and 18.1% more for gas when the energy company increases its prices on 13 September.
According to energyhelpline.com, this will cost bill payers an extra £170 a year and relegate 140,000 homes into fuel poverty.
The price hikes follow a 9% increase to electricity costs and 3% gas increase by the provider in February this year.
This summer British Gas, Scottish Power and Scottish & Southern Energy have all announced further bill hikes and although it's not surprising E.ON has followed suit, customers will still be hit hard, says Paul Green, chief executive of energyhelpline.com.
"Even though this price rise was fairly predictable, the scale of it will stun E.ON customers," he says.
"We have been warning this would happen for several months now because of the inflation in wholesale energy prices, but its predictability doesn't make it any easier for those who will be on the receiving end," he adds.
Alongside these price hikes, E.ON has vowed its Age UK energy customers won't see any increases to their bills for another year and its most vulnerable customers on its WarmAssist tariffs won't be affected at all.
E.ON blames the increases on wholesale price volatility, with managing director Graham Bartlett citing events in Japan and Libya "having a dramatic effect on gas and power prices in a relatively short time".
He also refers to the Bank of England's inflation report, which reveals gas prices increased by 20% between February and May.
So what can you do?
Green urges consumers to consider fixing:
"This price rise should serve as a further warning to people about the need to switch to a fixed-price energy deal as soon as possible."
Check out the Moneywise Energy Switcher to see if you could save money on your utility provider
"By going to a price comparison website, you can save £643 over the next three years and have peace of mind that your prices won't go up until 2014."
Three quarters of British households are on unsuitable, standard tariffs, which cost them extra, according to Ovo, an independent energy provider.
"They are paying more than they need to because they are stuck on confusing standard tariffs," says Stephen Fitzpatrick, managing director of Ovo.
He is calling for industry regulator Ofgem to step in on behalf of consumers: "Energy is a necessity - but people do not have to accept these costs. It is time for Ofgem to help consumers fight back by injecting competition to challenge the dominance of the 'Big Six' and put a cap on energy prices."