SSE customers are to be slapped with a 6.9% increase in the price of their dual fuel bills, a move that will see £73 added to their household costs.
The energy giant said the hike is the result of an average 14.9% electricity price increase and will impact 2.8 million customers.
SSE pinned the rises on the increasing cost of supplying electricity, and specifically higher costs associated with delivering Government programmes designed to upgrade "Britain's ageing energy infrastructure".
The energy giant said the increase will come into place on April 28.
Will Morris, SSE's managing director for retail, said: "We deeply regret having to raise electricity prices. This is the first increase since 2013 and we've worked hard to keep them down for as long as possible by cutting our own costs, putting in place a winter price freeze and holding gas prices, but we have seen significant increases in electricity costs which are outside our control.
"Without an increase, we would have been supplying electricity to domestic customers at a loss."
SSE said that it will establish a £5 million fund providing "targeted financial assistance" to minimise the impact on vulnerable customers.
A typical dual fuel bill will now cost SSE customers £1,142 per year and the firm is the latest of the Big Six energy suppliers to announce price hikes.
Eon, ScottishPower, Npower and EDF have all ramped up prices over the past months, hammering households already struggling with rising inflation linked to the Brexit-battered pound.
In better news for hard-up families, British Gas has announced it is to extend a price freeze for customers on its standard energy tariff until August.
Mark Todd, co-founder of switching service energyhelpline, criticised SSE's move.
He said: "The £73 hike is a hammer blow to households with many already struggling to make ends meet.
"However, it can be avoided if customers switch to a cheap fixed rate energy tariff. Energy is the easiest big bill to control - comparing and switching only takes five to 10 minutes. No-one needs to suffer this price rise if they really don't want to."
The Government and the energy regulator have also weighed in to the debate, with Prime Minister Theresa May's spokesman saying earlier this year that she is "concerned" about soaring energy bills.
Ofgem, meanwhile, has said that it does not see "any case" for significant price increases where suppliers have bought energy in advance.