The government is being accused of expecting charities to do an increasing amount of the core work its agencies should be doing.
The Council of Christian Social Services said in the past year a lot of complex work had shifted from Child Youth and Family to non-government organisations, with no funding increases to match.
Executive officer Trevor McGlinchey said his members would say that over the past five to 10 years the increase in demand has escalated considerably as has the complexity of the work.
"In the last short while, Child Youth and Family has undertaken its own workload review and has decided some of the work it used to do is best done by non-government organisations.
"So over the last year or so, quite a lot of quite complex work has been shifted from Child Youth and Family to non government organisations. And that's without an increase in funding."
Mr McGlinchey said he knew of one service in South Auckland contracted to deliver home services to young children.
He said its workload had increased significantly but its budget had not.
"When they tallied up all the children they'd actually directly worked with and made a difference for over the year, it was around 2000.
"They were funded for 365 kids, they worked in the same focussed way with 800 children, but overall they affected the lives of 2000 kids, for the funding of 365."
Mr McGlinchey said there had been few inflation increases in the past seven years, though costs have risen 13 percent.
Minister for Social Development Anne Tolley told Radio NZ's Insight programme yesterday that matching funding to inflation was not a good funding model, and it was introducing outcome-based contracts.
"We've funded them on an input, how many meetings can you have, how many people can you deal with. That's not a good way of working for them, or for the government," she said.
As part of this review for the Community Engagement Strategy, the Ministry of Social Development is currently reviewing how it funds 2000 non-government agencies.
Mrs Tolley said the strategy would create a more results-focused and evidence-based approach for the Ministry's purchasing of social services for vulnerable people and communities, and would also be more transparent, targeted, flexible and efficient.
"What we've got are those three areas that we've identified - vulnerable adults, vulnerable youth and vulnerable children and so it's where is fits in all of that.
The Ministry is working with providers over the next three years to help them transition to new contracts and this should be completed by 2018.
Tomorrow the Productivity Commission will release its final report into the delivery of social services.