Shadow treasurer Chris Bowen wants to make sure Labor's policies are watertight when the next federal election is called.
Delivering his budget reply speech on Wednesday, he said the independent Parliamentary Budget Office should be treated with the same respect as Treasury when it comes to costing policies.
But that hasn't stopped Labor employing the additional scrutiny of three eminent experts.
"As the opposition, I think it's right that we just apply that extra piece of rigour," Mr Bowen told the National Press Club in Canberra in answer to a question.
Labor has re-hired academic Bob Officer, former public service chief Mike Keating and businessman James MacKenzie to check the party's policy costings and assumptions.
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In opposition, parties do not have the benefit of Treasury exclusively checking out their policies.
However, Mr Bowen is concerned when a government uses Treasury to cost an opposition's idea for use in political debate.
"They should not be a political battering ram, and there is a pattern of this Treasurer (Scott Morrison) commissioning Treasury work, releasing it selectively to some journalists and not releasing the full work for full proper scrutiny," Mr Bowen said.
"That is a politicisation of the Treasury which is not on."
Mr Bowen, who is about to be in the unenviable position of being the second-longest shadow treasurer, pledged a Labor government will bring the budget back into the black in the same year as the coalition.
It will also deliver bigger surpluses and pay down debt faster over the next decade.
Mr Morrison announced in last week's budget the return to surplus would occur a year earlier than expected, in 2019/20.
Mr Bowen said the earlier return to the black was welcome, but Australia needed a bigger buffer to withstand future downturns in the global economy or a trade war.
He said the 2019/20 surplus of 0.1 per cent of GDP predicted in the budget can be "blown over in a light breeze", never mind a major headway from events overseas.
He said that surplus only comes about by a "massive bring-forward" of tobacco excise of $3.3 billion, while assuming wages growth suddenly jumps out of the rut it has been in for years and back above three per cent.
"The whiff of a surplus, not reaching at least one per cent of GDP until 2026/27, does not adequately protect Australia against the potential roiling seas of international uncertainty."
