Two key planks of Malcolm Turnbull's policy platform face make-or-break decisions when parliament returns after the long winter break.
The unpopular corporate tax cuts will go to the Senate in the second week, with a number of government MPs pushing for the policy to be dropped if it can't get through.
Crossbench senator Derryn Hinch says he's open to the corporate tax cuts being limited to businesses with revenues lower than $500 million a year, but the government has so far ruled that out.
Mr Turnbull and Treasurer Scott Morrison are committed to cutting corporate tax rates but they have stopped short of promising to take them to the next election.
The other difficult policy for the government is the National Energy Guarantee, which Mr Turnbull has to sell to his own party room.
After a decade of policy indecision, the prime minister is aiming to lower power prices and restore investment certainty with the agreement.
But Labor state governments fear, even if they do back it in principle, the policy could be changed by pro-coal climate change sceptics in the coalition party room.
Liberal Democrats senator David Leyonhjelm's bill to restore the rights of the ACT and NT to have their own voluntary assisted dying laws will take precedence in the upper house on Tuesday.
But even if it passes the Senate, it is unlikely to be voted on in the lower house despite the bitter falling out that could cause between the government and Senator Leyonhjelm.
The Greens have vowed to try to censure Senator Leyonhjelm over his "sexist and vile" slurs towards Sarah Hanson-Young.
Senator Hanson-Young is also suing Senator Leyonhjelm for defamation after he made comments about her private life in the media days after telling her to "stop shagging men" in parliament.
After five by-elections, returning MPs in Braddon, Mayo and Fremantle will be sworn in, but results will be tallied over the weekend in Perth and Longman.
The by-elections did not change the numbers in the lower house, meaning Mr Turnbull still has a one-seat majority.
It will be the first sitting week since Labor MP Emma Husar revealed she will retire at the next election, bowing to pressure over a scandal around bullying and harassment in her office.
It's expected the coalition will still pursue the issue in parliament, while Labor will ask questions about a $444 million grant given to the Great Barrier Reef Foundation without any tender process.
