The Government was accused yesterday of using the cap on public service recruitment to justify more and more outsourcing of public services.
Delegates to the Impact conference passed a large number of motions condemning the increased use of outsourcing to deliver services.
They also criticised the use of voluntary agencies to provide public services at "cheaper rates of pay".
Impact national secretary Louise O'Donnell said the union did not accept the "ideologically-driven idea" that the private sector was always more efficient than the public service.
"We are increasingly concerned at the piecemeal privatisation and serial outsourcing being proposed, and in some cases implemented, in every area of our public services.
"We are sick of seeing an artificial cap on public service recruitment, imposed by the Government and enthusiastically supported by the Department of Finance, being used to justify more and more private provision, which usually costs the taxpayer more, while damaging services."
Ms O'Donnell, however, said Impact had to "box clever" in opposing increased outsourcing by recognising there were situations where the private sector had a positive contribution to make.
"Our bottom line must remain that proposals for outsourcing can be considered only if it can make a genuine positive contribution to high quality and accessible public services."
Impact has been embroiled in a major outsourcing controversy this year over its opposition to a Government plan to use a private company to reduce waiting times for driving tests, of up to a year at some centres.
The Civil Service Arbitration Board upheld a claim by Impact and another union, the CPSU, that the outsourcing of driving tests was precluded under Sustaining Progress as the testers were doing core civil service work.
In an address delivered in the presence of the Taoiseach, Impact general secretary Peter McLoone said the subject was an emotive one for the union.
"Not least because elements of the Government, Opposition, media and others have recently demonised this union and a group of our members, the driver testers, over the issue of outsourcing and waiting lists," he said.
"It has been a genuinely hurtful experience for this organisation, with its long record of pragmatic flexibility in the public services, to be singled out and vilified in this way."
Mr McLoone said criticism of the testers was "incomprehensible" when they had "unflinchingly" abided by the Sustaining Progress provisions on outsourcing and had never strayed from the State's industrial relations machinery in pursuing their case.
