SSE is to increase its household gas and electricity prices from 1 April, the first energy supplier to announce a price rise this year.
The move is a response to sustained rises in external costs that the company said are outside its control including charges for running the transmission and distribution network.
The changes will mean the standard price of electricity will increase by 6.2% a week, equating to a €1.21 per week rise.
Gas prices will rise 4.5% or €0.62 a week, with a typical dual fuel household bill rising 5.5% or €1.84 a week.
SSE Airtricity said the increase is its first since 2018 and follows a price reduction last summer, and price freeze through winter.
"Pass-through charges are outside our control and unfortunately have increased considerably - including electricity network and market charges," said David Manning, Director of Home Energy at SSE Airtricity.
"With our winter price freeze we did everything we could to minimise the impact of these increases on customers and, as we have done in the past, we will pass on any future decreases as soon as we can."
SSE Airtricity had previously reduced its electricity prices by 2.7% and gas prices by 11.5% around this time last year.
"SSE Airtricity is the first supplier to announce a price hike in 2021 after most of the suppliers committed to a winter price freeze late last year," said Darragh Cassidy from bonkers.ie.
"SSE is the third biggest energy supplier in Ireland behind Electric Ireland and Bord Gáis Energy so this increase will be felt by hundreds of thousands of customers," he said.
"And it comes at a time when energy use at home has probably never been higher due to us all being stuck indoors due to lockdown and when many might be struggling financially due to losing their job," he added.
Eoin Clarke from Switcher.ie said the increase is likely to be just the beginning of what's to come.
"It's going to feel like a bit of a sting to consumers, many of whom are already struggling," he said.
"This is a really worrying time for many people, with high levels of unemployment, paying the bills is a struggle for many families."