Putting itself on a possible collision course with the Senate elected in 2016, shadow treasurer Chris Bowen has confirmed a series start dates for Labor's ambitious tax agenda, with many proposals due to kick-in from July 1 - just six weeks after the expected election on May 18.

The deficit repair levy on Australians earning more than $180,000 a year, a minimum 30 per cent tax rate on distributions from discretionary trusts, and an overhaul of franking credits are among the tax proposals needing parliamentary approval.

​Changes to the low and middle income tax offset announced in last week's budget also need to be made law before the end of the financial year, with the Australian Tax Office confirming the laws need to be in place as soon as practicable if people are to receive the $1080 rebate from July 1.

MPs now expect a special sitting on Parliament in the last week of June that would include senators who were elected at the 2016 poll but may have lost their position at the 2019 election. Those senators would still be entitled to vote on legislation until the new Senate convenes from July 1.

Mr Bowen said a Labor election win would give it a mandate to implement its tax agenda.

"That is, I think, the necessary opening part of the conversation with the Senate crossbench," he said.

"That doesn't necessarily mean they automatically support our policies. But it is the essential door opener to the conversation.

"We (will) start with a moral authority of a mandate from the Australian people."

Under the current Senate, Labor could get enough support from the Greens, Derryn Hinch, the Centre Alliance block and South Australian independent Tim Storer to pass the deficit levy, which has been estimated to raise $6.2 billion over a decade by imposing a two per cent impost on workers earning more than $180,000 a year.

Labor has said the levy would remain in place until the budget surplus amounted to 1 per cent of GDP. Under the government's latest budget, that has been pushed back until 2026-27.

Its plans for negative gearing, family trusts and franking credits would also need to be passed relatively quickly but Labor faces a tougher battle to win crossbench support for those changes. Combined, these tax changes are forecast to raise almost $20 billion over the forward estimates.

Mr Bowen said Labor would deliver larger surpluses than those promised by the Coalition, citing Parliamentary Budget Office analysis that showed the government's stage two and three tax cuts -scheduled to commence in 2022 and 2024 - will cost $286 billion over the following six years.

Labor is opposed to both stages.

The shadow treasurer said Labor would consider tax cuts for both workers and businesses but only when the budget was in a stronger position.

Prime Minister Scott Morrison accused Labor of trying to put "weights" on the national economy.

"Over the last six months I've taken up swimming laps. Now if anyone said to me, 'you know, you'd go a lot faster if you put a weight belt on,' what do you think I'd say to them? It's hard enough," Mr Morrison said.

"But that's what $200 billion of higher taxes will do to our economy. It will slow us down. It'll slow you down."

SMH/The Age