The finance minister has told One Nation leader Pauline Hanson he won't negotiate on the coalition's tax proposal, as a Labor MP breaks ranks to support it.
The Morrison government has made it clear to crossbenchers the income tax cut package will be presented to parliament as a whole.
One Nation leader Pauline Hanson says she told Finance Minister Mathias Cormann on Thursday she wants the government to prioritise cutting power prices and boosting infrastructure spending.
"He said: 'I'm not negotiating with crossbenchers on this at all'," Senator Hanson told Sky News.
"He said: 'We have our three stages, we're going to pass that no matter what'.
"They're not prepared to actually look at it, listen to reasoning over this whole thing. I just don't think it's the best way to go."
The government will need four crossbenchers to support the three-stage tax package if Labor doesn't back it.
Otherwise it won't make it through the Senate when parliament resumes in less than a fortnight.
Acting Prime Minister Michael McCormack is urging all Labor MPs to follow in the footsteps of their colleague Peter Khalil, who wants the government's full tax plan passed if it remains unwilling to split it up.
"Come on over, Peter, come on over. Join the Liberals and Nationals," Mr McCormack told reporters in Victoria.
"He's sounded the alert that all Labor members should follow."
Labor supports the first stage of the $158 billion plan, which will mean extra cash for low and middle income-earners.
But it believes the later stage, aimed at flattening the tax rates by mid-2024, shouldn't be legislated years in advance and may benefit too many who are already wealthy.
The coalition has ruled out splitting up the package, arguing the later stage will bring much-needed structural reform.
Mr Khalil, the member for Wills in Melbourne's north, says Labor would prefer that the coalition ditch the later part of the plan.
" (But) in the scenario that looks increasingly likely, which is they will not split the tax cut package, my view is Labor should not block tax cuts that will benefit millions of working and middle class Australians," he said.
The government insists it has a mandate to pass the full tax package after its convincing election win.
"Peter Khalil has got it right," Mr McCormack said.
"He understands. Why can't (Labor leader) Anthony Albanese?"
Labor frontbencher Penny Wong said the coalition was holding up the crucial first stage of the package.
"You want the stage one passed, why don't you bring it forward and we'll vote for it," she told reporters in Adelaide.
The opposition has requested information about how much of the tax package will benefit those earning more than $180,000.
But Treasurer Josh Frydenberg this week rejected a request to provide the information, telling his Labor counterpart Jim Chalmers there was enough detail in the latest budget papers.