Opposition finance spokesman Andrew Robb says the Labor government will never deliver a surplus, labelling updated economic forecasts "dodgy".
Treasurer Wayne Swan said on Wednesday the budget surplus was expected to hit $3.1 billion in 2012-13, up from $1 billion.
But Mr Robb said the figures underpinning the forecasts were unreliable.
"We've seen today dodgy figures used to explain a dodgy tax delivered via a dodgy deal," Mr Robb told reporters in Melbourne.
"It is no more than an attempted political fix to get the Labor government through the election.
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"The massive debt and deficit figures remain unchanged, the reckless spending remains unchanged, the forecast of a surplus is still unbelievable.
"It confirms once again that a Labor government, this Labor government, will never deliver a surplus.
"They are taking us all for mugs."
