Malcolm Turnbull says it is his "determination" to pass tax cuts for middle income earners next year after the government has legalised same-sex marriage and set up a disclosure scheme for politicians' citizenship status.

"We've got the business tax cuts underway. Our focus now is on middle-income tax cuts," Mr Turnbull told reporters at a Sydney produce market on Tuesday.

"We've got to manage that so we get the Budget back into balance - not going to walk away from that.

"Our determination is to ensure that we have more dollars left in the pockets of hard-working Australians.

"This is going to be our focus next year. Obviously we've got the Budget coming up, as always, in May."

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The announcement, first flagged when Mr Turnbull gave a speech to the Business Council of Australia on Monday night, comes as the government approaches the final sitting fortnight of parliament.

The government recently cancelled next week's scheduled sitting of the House of Representatives, pushing the final sitting back by one week.

The Coalition says it wants more time to guarantee the passage of the same-sex marriage bill and the citizenship register.

But the Labor opposition, Greens and crossbench have all accused the government of trying to buy time and avoid a vote on an investigative commission into the banks, while former deputy prime minister Barnaby Joyce fights a by-election in New England.

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Labor leader Bill Shorten said the promised tax cuts were a cheap attempt to shore up the prime minister's leadership and standing in opinion polls.

"It's like free beer tomorrow, isn't it?" he told Channel Seven.

"This bloke who just says whatever comes into his head to keep the wolves from the door."

Labor has also accused the government of contradictory policy on tax, given the government's decision at the last Budget to increase the Medicare levy - which applies as an extra income tax - by 0.5 per cent for nearly all taxpayers.

The Budget measure is still yet to pass the Senate.

"If Malcolm Turnbull wants to talk about cutting personal income tax, the first step he should take today is to drop his legislation to increase income tax to start with," Labor's shadow treasurer Chris Bowen said.

Mr Bowen said Australians were "feeling the pressure" from slow growth in wages and could not afford the increase in the Medicare levy, but would not be drawn on whether Labor would support any additional tax cuts.

Government continues push on company tax

Treasurer Scott Morrison has written to hundreds of corporate leaders, insisting they cannot afford to sit on the fence when it comes to the government's enterprise tax plan.

The government has so far legislated a tax cut for businesses with turnovers of up to $50 million, leaving the remainder on a rate of 30 per cent.

Further cuts face a roadblock in the Senate with Labor and the Greens opposed to the full plan.

"We are not going to give multinationals a reduction in their tax. We don't think that's the way to go," Mr Shorten said on Monday.

"We would rather look after ordinary people than give the top end of town a tax cut."

- with AAP