Up to one million electricity customers are seeing their prices increase from Monday.
The previously announced price rises for Electric Ireland and PrepayPower kick in from April 1st.
Electric Ireland is increasing residential electricity and gas prices by 4%.
The company has said the increase is due to "sustained increases in wholesale energy prices."
Marguerite Sayers, executive director of Electric Ireland, said: "We helped our customers by not increasing our prices during the winter months when energy consumption is at its highest and people have the added financial pressure of Christmas.
"This resulted in a total saving of €21m for Electric Ireland customers".
"However, against the backdrop of much higher wholesale energy costs, we now reluctantly have to pass on some of these higher costs to our customers from 1st April 2019."
PrepayPower
While PrepayPower also blamed increases in wholesale prices for its price rise.
The company will pass on an increase of 3.9% in its electricity and 3.9% in its gas prices to consumers.
A spokesman for PrepayPower said: "We introduced the price freeze to give our customers certainty during the winter period when energy use is highest. But wholesale energy prices continue to rise and we have no option now but to increases prices from the 1st April.
"We are now are the last major supplier to announce such an increase."
PrepayPower has 7% of the domestic electricity market in Ireland.
Price comparison website Bonkers.ie has said there are three ways to save money on energy bills.
Pay less for energy by switching to a cheaper energy supplier, use less energy by monitoring consumption, and to make energy efficiency improvements around the home.
However it added that switching suppliers is the easiest way to save money "because gas and electricity suppliers almost always save their best rates for brand-new customers, which are heavily discounted compared to the standard rates a longer-term customer is paying."
It said customers could save €396 a year on average on energy bills just by switching supplier.
Household bills
It comes as recent research found that 65% of Irish consumers cannot afford to cover essential household bills with their regular income.
While almost four in 10 (38%) dipped into their savings to cover the costs last year.
The survey from Switcher.ie said people also turned to credit cards to pay for everyday bills - with 26% using plastic to cover the costs.
Just over 20% said they borrowed money from family/friends or the bank to cover the cost of bills.
Others said they used money given to them by family and friends (11%), while some (4%) have resorted to pawning or selling their belongings to make ends meet.
