One Newport charity said donations were down 20% and staff hours were having to be cut back
The voluntary sector is warning it faces "hundreds, if not thousands" of job cuts as the recession hits its fundraising, investments and grants.
Leaders of Wales' 30,000 voluntary organisations and charities said for many, money is already running out.
They warn service cuts for many people worst affected by the recession could be inevitable.
The Wales Council for Voluntary Action said public services would "grind to a halt" if the sector is hit hard.
The council's chief executive Graham Benfield told BBC Wales Dragon's Eye: "Different charities are affected in different ways by the recession - some are already seeing reductions in income from dividends, from fundraising, from legacies, and grants are beginning to dry up - in other words, the money is beginning to run out for many people.
"They are going to have to make people redundant, or reduce their services."
'Arbitrary cuts'
Asked how many jobs could be at risk, he said: "Well, we know we are talking hundreds, and possibly, in a worst context, we are talking thousands of people.
"Many services are dependent on, or delivered by, voluntary organisations, when we look at advice services, counselling services, look at many of the activities and services for unemployed people, they're actually run through the voluntary sector.
"Most youth, leisure and communities activities run by the voluntary sector. So it's massive."
Mr Benfield said there are several areas that public authorities should address immediately, warning against what he called "disproportionate and arbitrary cuts".
He said it was imperative to avoid a "slash and burn" policy adopted in previous recessions, where voluntary organisations were hit first.
Child poverty
Extra funding should be made available to organisations in areas like debt counselling, housing and homelessness services, which were seeing increases in demand.
Asked how Welsh public services would function without the voluntary sector, he said: "Wales would grind to a halt within days."
Social Justice Minister Brian Gibbons acknowledged the importance of the voluntary sector in delivering key assembly government policies including reducing child poverty and employment and training initiatives.
But he said the sector could not be immune from the wider economic circumstances, including the slowdown in public sector spending.
He added that the next economic summit would examine the social impact of the recession in Wales, and provide a steer as to where funding should be directed.
Paul Evans, manager of the Raven House Trust in Newport, which provides emergency furniture and food parcels, said the recession had dealt them a double blow - demand was up by a third but donations are falling.
Meanwhile, staff have been put on short time working.
The trust helped more than 8,000 last year, but Mr Evans said many people's situation had worsened dramatically.
He said: "I've even had schools now, asking us for food parcels, for people who have turned around and asked the schools - 'we don't have any food, is it possible you could give us some food'.
"There is a great need. I'm very disappointed I've had to put my lads on short time - they're used to the people they go out to see, because these people have got nothing, and the lads are very good with them."
Mr Evans said that the authorities were often content to leave the trust to fulfil vulnerable people's urgent needs, but that some core funding would make their lives very much easier.
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