Energy giant npower has announced an increase in household tariffs of 9.3% for electricity and 11.1% for gas.
The price rise will be imposed from December 1.
It is the third of the so-called big six energy firms to raise its prices in recent days.
On Thursday British Gas become the second major supplier of household energy to announce a rise in its prices – by an average 9.2%.
The company said its electricity and gas prices would rise by 10.4% and 8.4% respectively from November 23 – affecting 7.8 million households.
Rival SSE announced a price hike almost two weeks ago, raising its bills by 8.2% from November 15.
Prime Minister David Cameron has called the latest increase “disappointing” and urged households to try to save money by switching suppliers.
But critics say it is more important to lock into a fixed tariff to avoid future rises.
Npower Energy Bills To Go Up On December 1st