Just as much action can be expected outside parliament as inside when MPs return to Canberra for the final, and potentially historic, sitting fortnight of the year.
The High Court on Monday will hold a directions hearing into whether two senators - Family First's Bob Day and One Nation's Rod Culleton - were ineligible to be elected at the July double-dissolution poll.
The triggers for that election - bills to restore the building industry watchdog and set up a new Registered Organistions Commission - will be high on the government's legislation priority list.
"It will be a critical fortnight, indeed it will be potentially a historic fortnight," Attorney-General George Brandis told the Victorian Liberal Party's annual general meeting on Sunday.
"Before the Senate we will be fighting a number of absolutely key battles to keep Australia safe and secure and to keep our economy prosperous."
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The eligibility of Mr Day, who has resigned from the Senate, and Senator Culleton have the potential to change the dynamics of the upper house as their replacements could take a different approach to the government's plans.
The coalition has greater confidence its registered organisations bill will pass with the support of Senate cross benchers, but there is less certainty about the Australian Building and Construction Commission legislation.
Labor's workplace relations spokesman Brendan O'Connor believes it's possible the first could succeed, but it would need serious amendments.
The party will be pushing for them to include letting ASIC be the regulator, exempting volunteers, better protection for whistleblowers and having the same donation disclosure thresholds for candidates in unions and MPs.
On the ABCC, crossbenchers have told him they have significant concerns, but Mr O'Connor conceded on ABC TV: "who knows where it will land at this point".
With Mr Day no longer in the Senate, the government will need eight crossbench votes instead of nine.
If One Nation's four senators and Nick Xenophon's three are on board, the government will then only need to convince independent Derryn Hinch or the Liberal Democrats' David Leyonhjelm.
The House of Representatives will kick off the week with debate on private bills to protect Christmas Day pay rates in Victoria and legislate for same-sex marriage.
Prime Minister Malcolm Turnbull won't be in parliament on Monday, as he attends the APEC summit in Peru, with his deputy Barnaby Joyce stepping into the top role.
The election of Donald Trump as US president is likely to be the focus of attention in question time, with Labor railing against American-style policy and the coalition arguing for business tax cuts and workplace reform to drive economic growth.
Superannuation will be on the agenda midweek when a Senate inquiry reports back on the government's reforms and Labor will seek to make amendments.
Uncertainty still hangs over the so-called backpacker tax after 18 months of debate and proposed changes from the government to drop the rate to 19 per cent.
Labor, the Greens and crossbenchers are seeking a 10.5 per cent rate, which could provide room for compromise.
