Len Brown's Auckland Council has spent more than $5.1 million on pollsters and surveys in the past three years.
A council spokesman said about 60 per cent of the spending was required under law, mainly for annual planning and reporting.
But councillor Cameron Brewer said spending on pollsters was "out of control".
Brewer said: "Think of the improvements a local park or playground could've enjoyed with this money. Instead it's all gone into lining the pockets of private pollsters."
The figures were released to Brewer under the Local Government Official Information and Meetings Act.