Just 11% of rental properties available in December accepted the Housing Assistance Payment, according to Simon Communities of Ireland.
The latest 'Locked Out' report by Simon shows that while the number of properties on the rental market has increased, there has been a fall in availability on the HAP scheme.
Of 1,349 properties available to rent in December across 16 areas including major cities, just 148 or 11% fell into HAP categories.
This is a 22% drop on the number available in October 2021 and "a drastic 83% less than the 906 available in June 2021".
Head of Policy and Communications at the Simon Communities of Ireland Wayne Stanley said the organisation looked at HAP in the report as it is a way for many people to leave homelessness.
Speaking on RTÉ’s Morning Ireland, he said: "When you look at homelessness, you look at the fact that if you want to address this, you have to prevent people coming in the first instance and support people out, and the HAP is a mechanism for people who are in housing need on low incomes."
The fall to 148 properties available to people on HAP is incredibly worrying, Mr Stanley said, because it further shows that the affordability crisis in the country’s housing system is "really, really acute".
The shortage of housing does often result in discrimination against those on HAP, he said, as if there are only 148 properties none are ringfenced for people on HAP.
Mr Stanley said that HAP is a mechanism for people to support them to pay their rent, but it really needs to be looked at in terms of its availability.
He added that local authorities outside of the Dublin region need more discretion around the payment, and the payment should be increased.
He said while it is a significant amount of money paid to people, it is not enough to offset the costs of the high rents in the market.
If the HAP payment increased it would just be "catching up" with the "unaffordable rents", he said.
"But if we don't do it, we're putting the burden of those rents on the poorest and most vulnerable in our society", he added.
The national housing charity said the figure represented a 16% increase on the same time the previous year.
During October, November and December, Threshold said it stopped 905 households around the country entering homelessness, which included 1,250 adults and 735 children.
The housing charity said its advisers challenged invalid notices of termination, invalid rent increases and assisted clients to resolve rent arrears.
