Treasurer Wayne Swan on the weekend said Treasury figures indicated a $9 billion hit to the economy from the summer of natural disasters across Australia.
"The latest figures back that up, and indicate the cost is likely to be even larger than we initially thought," Mr Swan said in an economic note.
The government has suggested there'll be some pain in the May budget in order to return a surplus by 2012/13.
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But Senator Brown isn't impressed.
"It's a very harsh budget from Treasurer Swan that's been flagged almost daily now," he told ABC Radio on Monday.
"That concerns me greatly."
The Greens are opposed to plans for a one per cent company tax cut, which Labor says will fund increases in employer superannuation contributions.
Senator Brown said this measure, which he estimates will cost $18 billion over the next decade, would come at the expense of other more worthwhile programs.
"We think it's unnecessarily harsh on average Australians," he said.
"That's a matter that's going to lead to some tension between the Greens and Labor in the coming months.
"I have no doubt we're going to be there to defend the interests of average householders and small business."
Prime Minister Julia Gillard's attack on the Greens, in which she said it was a party of protest that failed to relate to average Australians, was continuing to stir tensions in the minority government.
Senator Brown said Ms Gillard's Gough Whitlam Oration, delivered last week, was offensive to the 1.5 million Australians who voted for the Greens.
"She's used some language there on 1.5 million Australians and voters indicating, for example, they don't have love for family or love of nation, which is clearly insulting," he said.
"I can't imagine why Prime Minister Gillard did that. I wouldn't use that language against Labor voters or against conservative voters."
But Senator Brown said his party would be unlikely to reconsider its support for a minority Labor government.
"Our job is not to take offence from what other politicians say."
