A new public audit bill proposed by the Welsh government "confuses what accountability is" warned David Rees from Prospect.
Mr Rees voiced concerns that the new bill "restricts the Auditor General for Wales's freedom to act".
He stressed that "the bill needs to enable him to act as he feels fit but at the same time be subject to scrutiny".
"We have called for greater accountability over the years but this bill would make him less accountable," he told AMs.
The intention of the bill is to modernise the governance and accountability of the public audit service in Wales which will include establishing a new Wales Audit Office as a body corporate with seven members.
According to Mr Rees there needs to be more distance between the auditor general and the new body.
Executive Director of the Institute of Chartered Accountants in England and Wales (ICAEW), Vernon Soare, also warned that if a problem emerged within the proposed structure it would be "very difficult to know if it's the Auditor General Wales at fault or the board at fault".
Ben Robertson of the PCS Union stressed that "executive responsibility has to rest with the auditor general".
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