A new survey carried out by the Simon Communities has found that 80% of rental properties are beyond the reach of people depending on State housing benefits.
It also found that there are less than half the number of rental properties available when compared to May 2015.
Speaking on RTÉ's Morning Ireland, spokesperson Niamh Randall said the survey was a snapshot survey carried out in ten areas.
It found 518 homes were available to rent during the three days the study was undertaken in August, down 19% from 637 at the same time last year.
102 of the 518 homes available for rent were within Rent Supplement/Housing Assistance Payment (HAP) limits, with just eight of these available for single people and 11 for couples.
"Of huge concern is the ongoing reduction in the availability of homes to rent down by 19% from August 2015 and by a shocking 55% since May 2015 when 1,150 homes were available to rent," Ms Randall said.
"The increase in the limits, which happened in July has made a difference, it's made a small difference. So 80% of properties that were available, were beyond the reach of people in receipt of rent supplement or HAP payments.
The report is the first since changes to the rent supplement payment were introduced by Minister for Housing Simon Coveney last July, and seems to suggest the increases have had little impact.
The number of properties available to people in receipt of these payments increased by 54 homes since the same time in August 2015.
Ms Randall called for initiatives to be put in place to keep people in their homes and to increase supply in the private rental sector, with possible tax breaks for landlords, rent certainty and an increase in tenure to prevent people being pushed into homelessness.
"What we've called for, and we repeat our calls, is for rent certainty, where rents are linked to the consumer price index. That would reduce the volatility in the private rented sector. It would have much more certainty both for tenants and for landlords alike."
She said that rental accommodation should not be treated as simply a stepping stone to owning a home.
