The Turnbull government's personal income tax cuts have passed their first hurdle.
The opposition backed a new low and middle-income tax offset that would provide $530 relief each year and the lifting of the 32.5 per cent tax bracket from $87,000 to $90,000, both due to begin July 1.
But shadow treasurer Chris Bowen failed in a bid to separate those changes from further reductions in 2022 and 2024, on which Labor wants more detail and a potential Senate inquiry before considering.
"Do not hold the 2018 tax cuts hostage to the 2024 tax cuts," he told parliament on Tuesday night.
The amendments were defeated but the legislation will now move to the Senate where the split could again be pursued.
Treasurer Scott Morrison did provide some further insight into the cost of the tax cuts, breaking it into stages.
Parts one and two, which include the July 1 changes and part of the later cuts, will cost $102 billion over the medium term.
The final stage will cost around $40 billion, bringing the total to $143 billion over 10 years.
New Liberal senator Amanda Stoker had hinted a cost breakdown was coming.
"If we can negotiate with Labor to get this over the line, that would be ideal," she said.
Also before the Senate is the government's corporate tax plan, which Prime Minister Malcolm Turnbull remains confident about even as Pauline Hanson digs in her heels and insists One Nation won't back it.
Senator Hanson pulled out of an agreement with the government on Tuesday to support a reduction in the corporate tax rate to 25 per cent, blaming poor budget management and laxity on immigration.
Asked on Wednesday whether there was any chance of her reconsidering her position, Senator Hanson said: "No, it won't be reconsidered whatsoever."
"I cannot in all good conscience hand out a corporate tax cut to multinationals," Ms Hanson told reporters in Melbourne.
The government needs the backing of One Nation to help pass the tax plan with Labor, the Greens and other crossbench senators opposing the bill that would reduce the business tax rate from 30 per cent.
Mr Turnbull repeatedly side-stepped Labor's demands to reveal the deal that had been struck with Senator Hanson during parliamentary question time.
"We are always filled with optimism," Mr Turnbull told parliament.
"We are committed to a positive and respectful approach to the crossbench, to do all we can to ensure that our budget and other measures are passed through the parliament."
