Opposition Leader Bill Shorten is under government pressure to reveal Labor's position on legislated tax cuts for companies with annual turnovers between $2 million and $10 million.
"Tell us today, end the mystery" Treasurer Scott Morrison demanded on Sky News, a day after Mr Shorten announced a Labor government would repeal a cut in the corporate tax rate that applies from July 1 for companies with turnovers between $10 million and $50 million.
The decision will affect about 20,000 businesses and retrieve about $20 billion in lost tax.
Mr Morrison said more 100,000 businesses employing three million people were in the $2 million-$10 million range.
Labor, so far, has only committed to support a cut in the corporate rate - from 30 per cent to 27.5 per cent - for small businesses with a turnover up to $2 million.
The government has two scheduled sitting days before the long winter break to convince the Senate to approve the remainder of its 10-year business plan.
It has only secured the backing of four-of-the-eight crossbench senators needed to pass legislation that would cut the corporate tax rate to 25 per cent from 30 per cent for all firms.
Finance Minister Mathias Cormann, who is the government's chief negotiator in the upper house, says the government remains committed to securing its passage.
"We are not in charge of our own destiny in the Senate but that is certainly our intention," he said.
Senator Cormann also ruled out a compromise deal that would limit reductions to businesses with a turnover of up to $500 million, as backed by independent Derryn Hinch, because he would then lose the support of fellow crossbencher David Leyonhjelm.
Senator Hinch is sticking to his guns.
"I haven't changed. I don't intend to," he told ABC TV.
The two Centre Alliance senators haven't budged in months in their opposition to the tax plan, neither has independent Tim Storer.
The government fell short two votes when it tried to get the tax plan passed just before Easter, but One Nation has since reneged on a previous deal to support the cuts.