Treasury head John Fraser is happy to reveal the total financial impact of the Turnbull government's personal income tax cuts, but is not willing to provide a yearly breakdown.
Labor wants to see detailed costings as it weighs up whether to support the whole tax cut package in parliament.
"Our confidence in specific years is not such that we feel comfortable providing those figures," Mr Fraser told a Senate estimates hearing on Tuesday, in response to a question from Labor senator Jenny McAllister.
He did provide details to the hearing of the cost of the three-stage plan over 2018/19 to 2028/29 - step one being $16 billion, growing to $102 billion under step two and totalling $144 billion after step three.
The budget papers show the costing of the tax cuts until mid-2022 which amount to $13.4 billion, but do not include a bulk of the package from July 1, 2022.
Deputy secretary of Treasury's revenue group Maryanne Mrakovcic confirmed to the hearing there is a significant cost that occurs outside of the four years of the budget forward estimates.
"We do understand the importance of getting some sense of the medium-term cost of the policy to assist in the public debate and I think that is why the estimate of the $144 billion cost over the medium term has been used," she said.
"By the same token, we do understand that there is a considerable and heightened degree of uncertainty that does attach to the estimates the further out you go and in that sense, we have been reluctant to see those very specific point estimates out there in the public debate."
Senator McAllister asked if Treasury had yearly figures, but has chosen not to release them, to which Ms Mrakovcic said, "Yes, that's correct."
Speaking to journalists outside of the hearing, shadow treasurer Chris Bowen said he respects the Treasury secretary is acting on instructions from the treasurer, but questioned what Scott Morrison has to hide.
"He demands, huffs and puffs and beats his chest, and demands we wait for them and says 'I'm not going to give you the figures'," Mr Bowen said.
"The treasurer should treat the parliament and the people with greater respect."
