The Morrison government is not backing down on its plan to put its full $158 billion tax-cut package to federal parliament next week.
The coalition's determination comes despite Labor confirming it will only support the first two parts of the three-stage tax relief plan.
The government needs the support of Labor or at least four crossbenchers to get the full package through the Senate.
Labor has always backed the first stage, which will deliver extra cash to low and middle income earners when they file their tax returns this year.
But it says it will only support the second stage - also aimed at people on low and middle income - if the government brings it forward to the 2019/20 financial year, rather than 2021/22 as planned.
It also wants the government to defer legislation on the third part of the package which is due to begin in 2023/24, suggesting it is too far down the track amid uncertain economic conditions.
The third stage will reduce the tax rate from 32.5 per cent to 30 per cent for people earning between $45,000 and $200,000.
