Focus Ireland has criticised the agency for failing to deliver on its promise to use vacant units to help those with nowhere to live.
The charity says 5,000 people are currently homeless in Ireland and many of them are families living in emergency accommodation, such as shelters and B&Bs for 10 years or more.
And it says the number of families losing their homes every month in Dublin has doubled from 8 to 16.
The charity is holding its annual conference today and says it has seen an 18% increase in people seeking support this year. There has also been a 43% jump in the number of people contacting Focus Ireland in an attempt avoid becoming homeless.
The charity says it is vital that affordable secure housing is made available so that the rise in homelessness is stemmed.
Minister Jan O'Sullivan says there will be quicker delivery of NAMA units from now on because the process has been simplified.
"The intention of the Government - and it's an intention we will fulfil - is to get 2,000 units from NAMA during the lifetime of the government," she said.
"We have over 300 over the line at the moment, and we've provision made for 450 next year - but we've simplified the process somewhat and I do believe that we will have quicker delivery of those NAMA units next year, and from next year onwards."