People on lower salaries will be worst affected by an increase in the carbon tax, according to Social Justice Ireland.
A new report recommends raising the tax from €20 to €80 per tonne by 2030.
This will, in turn, have knock-on effects on the cost of fuel and the likes of coal and gas.
"There are hundreds of thousands of people who are struggling at the margin of survival," said Dr Seán Healy, CEO of Social Justice Ireland.
"Over 15% of the population has an income below the poverty line.
"If (an increased) carbon tax comes in, these are the people that are most vulnerable.
"The proportion of their income that will pay towards carbon tax is much higher than the proportion that would be paid by wealthy people," he concluded.