The Peter McVerry Trust says the current situation is "unsustainable"
The average monthly rent now stands at over €1,100 - that's up €134 a month in the last year.
Daft.ie's latest report warns that prices are soaring as supply plummets.
Rents in Dublin are now 66% higher than at their lowest point in 2011, while outside the capital they are up 41%.
Between January and March, rents rose by 13.4% - with an increase of 13.9% in Dublin.
Availability continues to be a major issue, with only 3,100 properties available to rent nationwide on May 1st - compared to almost 4,000 three months previously.
Rents are continuing to rise above the previous 2008 peaks.
The report notes: "In Dublin, rents are now an average of 15.4% above their previous peak while in Cork and Galway cities, rents are 9.7% and 17.8% above levels recorded nine years ago.
"Outside the cities, the average rent is 3% above its previous peak."
Economist Ronan Lyons, author of the report, says there are some very concerning findings.
Speaking on Newstalk Breakfast, he explained: "We just have a growing population, and not enough supply being built.
"Is it healthy? Absolutely not. Is it sustainable? Well in the sense that we have strong demand there, then unfortunately this is going to continue.
"This is a problem that unfortunately is going to get worse before it gets better," he added.
Housing and homeless groups have been reacting to the latest figures.
Peter McVerry Trust CEO Pat Doyle argued: “The report paints a deeply worrying picture and shows the current situation is unsustainable. Tenants are under huge pressure, and those people who are dependent on the rental system for their housing needs are looking at rents that are up to 15% higher than the Celtic Tiger peak with the lowest number of properties to rent since 2006.
"Our concern is that rapidly rising rents this will lead to more tenants becoming homeless.”
The Simon Community said that the high rents and low supply mean that people are experiencing difficulties in "finding and sustaining affordable homes".
However, Stephen Faughnan of the Irish Property Owners’ Association claimed that the State has "punished landlords that kept their rents low".
He suggested: "Government interference in the market - including unfair tax treatment, closing bedsits, two year rent freeze, 4% rent control, complex legislative compliance - all have a long term effect, increasing costs and damaging the market."