Big businesses won't get a tax cut until well after five upcoming by-elections because the coalition can't get enough support in the Senate.
But Malcolm Turnbull has refused to say whether he has done a deal with Pauline Hanson's One Nation for her support once the July 28 by-elections are over.
Senator Hanson is trying to win votes in the Queensland seat of Longman and she has faced attacks from Labor over cutting taxes for big banks and multinational companies.
The coalition originally wanted the company tax cuts to go to a vote this week, but instead they deferred it until August 13 at the earliest.
"Has the prime minister struck a secret deal with the One Nation party to delay the vote giving $80 billion to big business until after the upcoming by-elections?" Labor leader Bill Shorten asked in parliament on Thursday.
Mr Turnbull refused to directly answer multiple versions of that question.
"We never discuss negotiations with the cross bench," the prime minister said.
A spokesman for One Nation said the bill failed to get up for a vote with or without the party's support.
"There's no deal with One Nation on company tax cuts," he told AAP.
The government needs eight crossbench votes in the upper house to get its company tax plan through parliament, but has only got four votes so far.
"We have not yet been able to secure the necessary support," Finance Minister Mathias Cormann told reporters on the last day of parliament before the winter break.
The coalition wants to cut the tax rate for businesses with turnovers of more than $50 million a year from 30 per cent to 25 per cent.
Senator Cormann said the government remained committed to the tax cuts.
"Who knows? We might have a more business-friendly Labor leader, all sorts of things could be different after the by-elections," Senator Cormann said.
The two Centre Alliance senators oppose the cuts and they haven't budged for months.
Centre Alliance candidate Rebekha Sharkie is contesting a by-election in her seat of Mayo, where support for a company tax cut sits only at about 25 per cent.
Senator Derryn Hinch and fellow independent Tim Storer also remain opposed.
Senator Cormann said the government would keep negotiating with senators, including cracking down further on multinational tax avoidance to appease Senator Hanson.
A poll published in The Courier-Mail showed two-thirds of One Nation voters in Longman support reducing the tax rates for all companies.