Big business tax cuts are on hold but Labor wants a guarantee Pauline Hanson hasn't done a deal to vote them through after the July 28 by-elections.
Large companies 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 for her support once the July 28 by-elections are over.
"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.
Labor senator Murray Watt called on One Nation to guarantee it won't vote for the corporate tax cuts ahead of the Longman by-election in Queensland.
"With Senator Hanson's record of flip-flopping, Longman voters will know her current position will change once their votes have been cast," Senator Watt said.
A spokesman for One Nation told AAP "there's no deal with One Nation on company tax cuts."
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, but it has only got four of the eight Senate votes it needs.
"We might have a more business-friendly Labor leader, all sorts of things could be different after the by-elections," Finance Minister Mathias 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.
