Senators John Madigan and Nick Xenophon.
Prime Minister Tony Abbott has the numbers to abolish the carbon tax.
John Madigan, the Democratic Labour Party senator, said on Friday he would back the carbon tax repeal bills, scotching reports that an alliance of three could frustrate the Abbott government's No.1 priority vote in the new Senate.
Senator Madigan said it was an ''absolute crock'' that he would join Victorian senator-elect Ricky Muir and South Australian independent Nick Xenophon in making their support contingent on the government retaining Labor's $1.6 billion automotive transformation scheme.
The government stripped $600 million from the assistance scheme in the budget.
''I have never spoken to Ricky Muir or anyone associated with Ricky Muir, and I resent people putting words in my mouth,'' Senator Madigan said.
He said the DLP had gone to the election promising to stand against the carbon tax and that position had not changed, even though he was concerned at what the cuts to the auto scheme would do to jobs as car makers General Motors Holden, Toyota and Ford cease production by 2017.
Senator Xenophon said he had not come to a decision on the carbon tax but said Clive Palmer's intention to block the government's Direct Action plan concerned him. He claimed there is an ''indirect link'' between Direct Action subsidies and the auto transformation scheme.
''There's a link to the extent that a lot of automotive component companies have an opportunity to be involved in new technology backed by funds for renewable energy and the abatement scheme,'' he said.
Mr Muir, who is due to meet with the government's Senate leader, Eric Abetz, next week, said through a spokesman he was concerned at the potential for thousands of job losses in the auto sector but had not decided how he would vote.
The votes of Mr Muir and Senator Xenophon would be of no importance if the Palmer United Party bloc of three does not alter its position by July 7, the first sitting of the new Senate.
The support of NSW senator-elect David Leyonhjelm and Bob Day of Family First in South Australia, along with Senator Madigan, would give the government the six of eight crossbench votes it needs.
Mr Abbott showed no willingness to negotiate on the fate of the automotive scheme with crossbench senators on Friday.
''There's $1 billion available to manufacturers and to the auto parts industry over the next five years, so the automotive transformation scheme remains in place,'' he said.
The government pulled $100 million from auto assistance in the current financial year, according to the budget papers, and another $100 million will be saved from June 30.