Prime Minister Julia Gillard has scoffed at the opposition's complaint that a Treasury analysis of its tax policies was leaked to the media.
Shadow treasurer Joe Hockey on Monday slammed the leaking of the "unsolicited" analysis and has written to Treasury secretary Martin Parkinson demanding an explanation.
It has since been revealed that the office of Treasurer Wayne Swan was the source of the leak.
Labor on Monday used the Treasury report to argue a coalition government would impose higher taxes on business.
The analysis showed three coalition tax policies would cost businesses $4.57 billion in the first full year of a Liberal-National government and $17.2 billion over four years.
The policies include imposing a 1.5 per cent levy on big companies to fund paid parental leave, axing the instant asset write-off and other tax breaks for small business funded by the carbon tax, and the abolition of the business loss carry-back policy.
Ms Gillard, speaking on the sidelines of the Asia-Europe Meeting in Vientiane on Tuesday, said it was "very routine for routine for Treasury to cost policies that are being talked about in the public domain".
She said the real issue was that businesses would face an added $4 billion burden in the first year of a coalition government.
"No amount of spin from the opposition gets away from the simple fact that three of the policies they say they have committed to have been costed and they will cost businesses more than $4 billion in the first year," she said
Mr Hockey said on Monday the figures were "grossly inaccurate", although he declined to say what Treasury assumptions were wrong.
In his letter to Dr Parkinson, Mr Hockey said "if Treasury undertook to conduct these unsolicited costings, or subsequently released these costings to the media, then the apolitical and non-partisan nature of Treasury has been severely compromised".
He also asked if Mr Swan's office had sought the costings and if Treasury was told it would be released to the media.
Mr Swan's spokesman said Mr Hockey should take responsibility for the impact of the policies and not blame hardworking Treasury officials.
"The onus is on Joe Hockey and the Liberal Party to prove that their massive tax grab will not smash the business community," the spokesman said.