As Mr Swan basked in the congratulations of his colleagues on Tuesday night, Assistant Treasurer Bill Shorten introduced draft laws allowing the government to increase the amount it can borrow from $200 billion to $250 billion.
The opposition's junior treasury spokesman Mathias Cormann said the government was on track to exceed a borrowing limit approved by parliament.
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"That would mean the government would be breaching the law as it stands," Senator Cormann told ABC Radio on Thursday.
He accused Mr Shorten of sneaking into parliament "in the darkness of night" to introduce Labor's legislation.
"This is just another example of incompetence, just another example of a government that has lost control of its budget," Senator Cormann said.
Mr Swan dismissed the coalition's accusations, saying the need to increase the ceiling was flagged at a mid-year budget review in November.
"There will be no surprise about this at all," Mr Swan told ABC Radio, adding the details had been on a government website for some time.
"The reason we are doing it is because of the impact on the budget of the natural disasters and more substantial revenue write-downs that have occurred in the first part of this year."
The government's low net debt of 7.2 per cent of GDP was "eminently affordable", Mr Swan said.
"Our net debt is one-tenth of the net debt of other major advanced economies.
"Of course, we will pay that debt off over time."
