The price and petrol and diesel is going up from midnight tonight as part of the latest increases in excise duty.
The price of petrol will go up by 4c per litre while diesel will increase by 3c per litre.
It is the second increase in three months following on from a similar hike in April.
It comes as the AA's monthly fuel price survey shows prices have already risen in July.
In July, average petrol prices rose slightly by 1c to €1.80 per litre, while diesel prices are up by almost 3c to €1.74 per litre.
Temporary cuts were introduced after the Russian invasion of Ukraine in 2022 but these are now being pulled back.
The Government initially planned to fully reverse excise cuts last October; however, it postponed the plan until this year.
Petrol and diesel prices on display at a Cork petrol station, 9-3-22. Image: AG News/AlamyIndependent Sligo-Leitrim TD Marian Harkin has warned the increase will hit businesses along the border hardest.
“On average, petrol is at least 10c per litre cheaper in Northern Ireland than the Republic, with diesel an average of 7c cheaper per litre," she said.
"When the price hikes of 4c per litre on petrol and 3c per litre on diesel come into force on August 1st, we are looking at a price differential of at least 14c per litre on petrol and 10c per litre on diesel.
"This means that motorists will cross the border in even greater numbers to buy their fuel and when there, many will also do their weekly shop in Northern Ireland."
Deputy Harkin branded the situation as "absolutely untenable".
"This will mean business closures and job losses along the border as forecourts in the Republic will be unable to compete on prices, and the loss of business to supermarkets and smaller shops in the border region will be hugely significant," she said.
"I am asking the Minister for Finance to do an analysis on the possible loss of revenue to the State, both in terms of overall lost revenue and likely job losses, because the worst possible outcome would be for the State to lose revenue while businesses along the border close," she added.
'Electric vehicles'
AA Head of Marketing Jennifer Kilduff said electric vehicle owners shouldn't feel the pinch so much.
"We saw a slight increase in petrol and diesel prices this month, which is not ideal for the motorist no matter how slight the increase," she said.
"There is some good news this month however for electric vehicle owners; they should see a reduction in their fuelling costs.
"This is largely due to the recent decrease in ESB charging rates as well as competitive 24-hour rates from energy provider YUNO Energy," she added.
Crude oil prices continue to remain around $80 per barrel.
