A "radical overhaul" has been demanded of Brecon Beacons National Park's planning department after a second critical report about its procedures.
Brecon and Radnorshire AM Kirsty Williams also made a fresh call for park managers to quit.
The latest report by Powys Council's audit services found failings weeks after a critical inquiry into an application for a caravan park.
The park said it was making changes and "starting to make genuine progress".
"We are starting to make genuine progress in changing how we deliver our planning services"
Earlier this year an independent inquiry, commissioned by the park, was critical of an application for a caravan park at Gilestone Farm in Talybont-on-Usk, near Brecon.
The national park apologised and promised changes, including appointing an independent adviser.
The latest report is from Powys Council's internal audit services, who were called in following the independent inquiry. It too identified a number of failings.
Liberal Democrat Ms Williams said: "If this report related to a school or social services department it would be put into special measures immediately.
POWYS COUNCIL FINDINGS INCLUDE:
"It is time for a radical overhaul of how the park's planning system is run and for those responsible to be properly held to account. Senior managers, more than ever, must consider their position."
She added: "Concerns about Brecon Beacons National Park Authority's systemic failings are refusing to subside, and this latest independent report highlights flaws within planning procedure across the board."
The national park's chief executive Christopher Gledhill said the concerns raised by Powys Council were already being tackled.
Energy
He added: "We are starting to make genuine progress in changing how we deliver our planning services.
"[Environment Minister] Jane Davidson has stated publicly that she believes we can make the necessary changes to turn around the planning service within the agreed timetable."
Mr Gledhill said Ms Williams knew how much energy and resources were being put in to make the changes, and he was disappointed by her comments.
The Welsh Assembly Government has also urged the park to improve the way it handles planning inquiries, which includes the appointment of an independent adviser last month.
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