Labor councillor Shayne Sutton made a complaint to the ombudsman after the council rejected her requests to access civic cabinet documents for 12 months.
"Cr Newman is now the most secretive mayor in Australia," she said in a statement on Monday.
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"I am extremely pleased the Queensland ombudsman has backed the Labor opposition's interpretation of council's local law, which states that the minutes of any council committee should be open to inspection by any Brisbane city councillor and members of the public."
But the victory is short lived - from July 1 the documents will again be exempt from release after the state government passed the new City of Brisbane Act.
"He has done everything he could to keep these documents secret, including lobbying the state government to make them exempt from Right to Information searches in the future," Ms Sutton said.
