The government is being accused of hiding the cost of partially privatising four state-owned energy companies.
Finance Minister Bill English has told parliament the total amounts of the contracts with banks and other financial institutions which are preparing the share sales are commercially sensitive but Labour says that isn't correct.
"Just so the public know, the total costs for selling their assets are $7 million this year, $66m next year and $17m the year after that," he said.
"Bill English either doesn't know what he's doing or is taking the public for fools."
Mr Cosgrove has released documents held by parliament's finance and expenditure committee which he says prove his figures are correct.
The government is going to sell 49 per cent of the shares in Mighty River Power, Genesis Energy, Meridian Energy and coal miner Solid Energy.
Shares in Mighty River Power are due to be floated in September.