Beneficiary Advocacy Federation spokeswoman Kay Brereton said substance abuse covered a broad range of problems, from those addicted to painkillers prescribed for a medical condition, to those with an illegal drug habit.
Long-term addicts were often using substances to cope with past trauma and could not become work-ready in a set timeframe. However, "semi-medical" staff at the Ministry of Social Development (MSD) had begun "second guessing" doctors' assessments and asking them to change their medical opinion in order to get beneficiaries back into work, she said.
While there was nothing wrong with MSD seeking more clarity on doctor assessments, it had to be transparent.
Work and Income associate deputy chief executive Liz Jones disputed the claims.
But she said staff regularly contacted doctors to clarify information provided on medical certificates or confirm benefit eligibility or work capacity.
Deputy chief executive Debbie Power said clients with a substance addiction had "deferred work obligations" until determined ready for work.
