Appeal comes as new regulations allow annual rent increases and market resets for new lets.
Threshold says HAP payments must be reformed to come in line with the Government's new rent regulations.
New rules for the rental market are in now place, with no existing tenancies affected.
Landlords can reset the rent to market rates for new tenants and increase prices every year by 2 per cent or the rate of inflation, whichever is lower.
John Mark McCafferty from Threshold says HAP recipients won't be able to keep up with these rises unless changes are made:

€1.5 Million Cannabis Seized In Joint Dublin Operation
Calls For Prison Security Review After Inmate Died In Their Cell
Fuel Oil Prices At Highest Recorded Value In Five Years
Over 200 Fines For E-Scooter Offences Issued In Kildare Carlow Area
Planned 72-Hour Ambulance Strike Called Off
Taoiseach Travelling To Vatican To Meet Pope Leo
Newbridge Scientist Hopeful For Ambitious Project Aimed At Preventing Hospital-Acquired Infections
Irish Rail To Scrap IT System Believed To Be Worth €50 Million