Opposition Leader Tony Abbott says the federal government won't ever return the budget to surplus because it's wasting money on transporting asylum seekers.
Mr Abbott says every boat that arrives in Australian waters costs taxpayers $13 million.
"Currently the government is spending more money flying illegal boat arrivals around the country than it is subsidising the Royal Flying Doctor Service," he told reporters in Sydney on Monday.
"That is the sorry pass we have come to in this country because we have a government that is incompetent and untrustworthy."
Business Council of Australia chairman Tony Shepherd has called on Labor to spell out a "clear plan" to deliver a surplus in 2012/13, rather than base its claims on Treasury forecasting.
Mr Abbott said the government is "crab walking away" from its commitment to deliver surpluses.
"A coalition government gets the budget into surplus, it pays down debt, it produces assets," he said.
"That is the kind of good economic management which provides the kind of social dividend which Australia came to enjoy under the Howard government."
Senior Liberal Christopher Pyne believes a coalition government would have kept the budget in surplus over the past five years.
The government has repeatedly said it will return the budget to the black, forecasting a $1.1 billion surplus this financial year and increased surpluses in future years, after four years of budget deficits.
"If there had been a coalition government for the last five years, I think most people accept that we would have had continuing surpluses," Mr Pyne told Sky News.
"We would have had money in the bank, as (former prime minister) John Howard left us with money in the bank."
Treasurer Wayne Swan agrees falling commodity prices will make it more challenging for the government to achieve a budget surplus, but says it remains the appropriate thing to do.
He declined to concede the budget could remain in deficit.
"I don't deal with hypothetical situations," he told reporters in Brisbane.
Mr Swan also had no intention of adjusting his budget forecasts in the near term.
"We don't redo our budgets every month when new data comes out," he said.
"We have a look at what's going on but where you've got an economy with low unemployment, growth around trend, strong investment pipeline, then it's appropriate we return to surplus."