The Civil Public and Services Union has accused the Government of promoting higher grades and ignoring promotions for frontline staff.
Speaking at the union's conference in Cork, General Secretary Eoin Ronayne said the Government had approved up to 60 promotions of higher grade staff in the Revenue Commissioners and the Department of Social Protection in recent weeks, at a time when frontline staff were under serious pressure.
He said those at the coalface - his members working in public offices - were not being replaced and there were very few low-level promotions.
Mr Ronayne also warned that proposals to reduce public service sick leave entitlements would cause difficulties for his union.
Negotiations between public service management and unions on reducing the annual public service sick leave bill of €500m will get under way at the Labour Relations Commission on Tuesday.
Delegates also voted to oppose any moves to impose further cuts in pay, pensions or increments.
