Shadow treasurer Chris Bowen says the federal government needs to acknowledge that its post-election spending promises are blowing out the budget.
Treasurer Joe Hockey is expected to unveil a 2013/14 budget deficit of just under $50 billion when he releases the mid-year economic and fiscal outlook in Canberra on Tuesday.
Treasury's independent pre-election budget update, released in August during the election campaign, showed the deficit on track for $30.1 billion.
That figure was fully acknowledged by Labor, Mr Bowen said.
"Every dollar above that Joe Hockey has to take responsibility for," he told reporters in Sydney on Monday.
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The treasurer had yet to justify why he gave the Reserve Bank $8.8 billion to top up its reserve funds, Mr Bowen said.
Added to that was $3 billion in tax breaks, changes to superannuation and a range of spending promises.
The surplus appeared to be going the way of the Gonski school funding reforms, the national broadband network and and buying asylum-seeker boats, Mr Bowen said.
"Saying one thing before the election and doing something very, very different after."
The Australian people were entitled to conclude the promise to return the budget to surplus and pay down debt was "a lie".
Labor would not give the government any "blank cheques" if it needed legislation to increase revenue, Mr Bowen said.
