The union IMPACT claims that 5,000 jobs have been lost in the community and voluntary sectors due to funding cuts of up to 20%.
Maeve McCarthy-Barrett of the union's Cork branch has said that the job losses represented about 10% of the workforce in the sector.
A report commissioned by IMPACT last year estimated that there were approximately 6,100 voluntary and community organisations in Ireland, employing over 53,000 people.
The report estimated that the value of the sector to the economy at €6.5bn.
Ms McCarthy-Barrett said remaining staff had also taken pay cuts and increased their working hours in an attempt to keep struggling services afloat.
The chair of IMPACT's Health and Welfare Division Sophia O'Reilly said the sector was needed more than ever as more people became marginalised and vulnerable.
The union has pledged continued resistance to cuts.
IMPACT has called on Government departments to make specific provision for salary, capital and programme costs when funding community and voluntary organisations.