And as Parliament returned for 2018, the Turnbull government stepped up its threat to use its numbers and unilaterally refer Labor MP Susan Lamb to the High Court over her dual citizenship, in what would be a significant break with parliamentary convention.

Labor's shadow cabinet was due to discuss on Monday evening whether it should formally adopt a position of opposing Adani's giant Carmichael coal mine. Some MPs expect that position to be adopted within a matter of days, before the date for the Batman byelection is set.

The Greens, for their part, have welcomed Labor's apparent shift on Adani - Mr Shorten said on Friday he was "increasingly sceptical" about the project - but urged a vote for their candidate, Alex Bhathal. The Adani mine shapes as a key issue in the contest and a major test of the ALP, which is desperate to hang on to what was a former heartland seat.

Buoyed by a slight rise in Newspoll, which saw the Coalition's two party-preferred vote improve from 47-53 to 48-52, Prime Minister Malcolm Turnbull and his senior ministers stepped up their attack on the Opposition Leader over Adani, Labor's opposition to company tax cuts, Mr Shorten's call last week to reconsider the case for a living wage and a possible cap on private health insurance increases of 2 per cent for two years.

Australian Chamber of Commerce and Industry chief executive James Pearson, who represents thousands of businesses across the country, said his members were increasingly concerned about "the tone and some of the specifics of the Leader of the Opposition's press club speech last week".

"In particular, the call for a huge increase in the minimum wage, styled as a living wage, to 60 per cent of median earnings ... that would represent an increase of over 26 per cent over four years, and quite simply that would overwhelmingly impact small business in Australia," he said.

"For many that would be a recipe for disaster. The risk is the uncertainty it creates now will impact on business' willingness to hire now, let alone in the future."

Mr Shorten targeted Mr Turnbull in question time for championing a "$65 billion tax cut [for big business] while increasing taxes on ordinary workers [by] up to $300 every year", at a time when company profits had risen by as much as 10 times the rate of wage increases.

But Mr Turnbull fired back that Labor was moving "further and further to the left" under Mr Shorten as "they race to hold the seat of Batman".

"The Australian Labor Party has now taken up this left wing anti-business, anti-free enterprise approach, which is calculated and indeed designed to destroy thousands of jobs, thousands of opportunities."

Greens leader Richard Di Natale predicted Labor would shift its position to formally oppose the Adani mine “in a matter of days and that “will be a good thing, it is something we have great pride in, that we are helping to lead national debate".

Senator Di Natale highlighted a number of other policies Labor had adopted from the Greens, including the banking royal commission, changes to negative gearing and, recently, support for a National Integrity Commission.

“Our job is to implement Greens policies, if they are adopted by the Labor Party that is a good thing.”

Earlier, Defence Industry Minister Christopher Pyne said it was "disgraceful and scandalous that Bill Shorten is so weak and incapable of acting like a leader that he doesn’t require Susan Lamb to resign".

"We will refer [Ms Lamb] if necessary, if Labor refuses to do the right thing," he told ABC radio. Inside the Coalition, however, some are uncomfortable with the precedent such a move would set as until now, MPs have always been referred to the High Court on a bipartisan basis.

Ms Lamb argues she took reasonable steps to renounce her British citizenship but has been unable to demonstrate the renunciation took place. The government argues Ms Lamb's own legal advice indicates she still holds British citizenship.

with Michael Koziol