Opposition Leader Tony Abbott says he will congratulate Wayne Swan if the federal treasurer delivers his promised budget surplus.
But only after he falls over with surprise.
Mr Abbott says Mr Swan should consider resigning if he does not deliver a forecast $1.5 billion surplus in 2012/13.
The current year budget is heading for a $37 billion deficit, up from the $22.6 billion forecast in May.
While the projected surplus, outlined in the Mid-Year Economic and Fiscal Outlook (MYEFO), has been described as "wafer thin", the treasurer prefers to call it modest.
"There is no doubt about that," he told ABC Radio.
Opposition treasury spokesman Joe Hockey says no one, except Mr Swan, seriously believes the government can deliver a budget surplus.
Mr Abbott went further when asked whether he would congratulate the treasurer if he managed the budget back into the black.
"Sure, I would be falling over with surprise, but then I would congratulate him if he delivers," he told reporters in Brisbane.
"If he doesn't deliver, will he be resigning in shame and embarrassment?"
Mr Swan defended his growth forecasts in the mid-year budget review despite his own warnings of dark clouds looming overseas.
But he admitted the world was not perfect when it came to forecasting.
Growth forecasts in MYEFO at 3.25 per cent for this year and next are lower than predicted in the May budget.
"What the Treasury does is makes its best judgment about the prospects for the year ahead, based on where we are at this point in time," Mr Swan said, adding the strength of Australia's domestic economy stood out in the world.
Some economists fear dimming global growth will impact on the local economy.
But the treasurer says the forecast takes into account a likely recession in Europe as well as growth in China being downgraded by "a little".
He says it's the same "trend growth" forecast as the Reserve Bank and international agencies, including the OECD.
Mr Hockey described the government's decision to impose a one-off 2.5 per cent efficiency dividend on the public service as "quite miraculous accounting".
The public service union says 3000 jobs will go as a result of the squeeze on government agencies.
Mr Swan said the coalition's plan to cut 12,000 public service jobs through a hiring freeze was a blunt instrument.
"They're being a little cute in comparing their policy to ours," he said.
Mr Hockey suggested the coalition would support the decision to reduce the baby bonus payment from $5400 to $5000, despite his leader saying it was a "rip-off of the forgotten families of Australia".
"We last time did not stand in the way of significant reductions in government expenditure as painful as it was," Mr Hockey said.
"It's a principle that we would apply again."
