More than 90% of homes for rent are beyond the reach of people dependent on state housing benefits.
A study by the Simon Communities in Ireland has found the number of rental properties has dropped dramatically and there is an increasing gap between rent supplement limits and prices.
National spokesperson Niamh Randall says benefits must be increased to allow people to compete in a very challenging market.
She said: "Also we found in terms of the overall availability of rental properties there was a drop from August 2017 when we last undertook the study of 15%.
This is a fall of 53% since May 2015 when we undertook the first study.
"So a really grim picture in terms of the private rental market and particularly for those on low incomes and those in receipt of state housing benefits."