Same-sex marriage and the future of dual-citizen senators will dominate the return of federal parliament.
During the winter break, a small group of Liberal MPs have been advocating for the party to drop support for a plebiscite on same-sex marriage, and instead allow a free vote on a bill in parliament.
However, conservative Liberals and Nationals MPs are urging Prime Minister Malcolm Turnbull to stand by the plebiscite which was taken to the 2016 election, and remains the preferred option among voters to deliver change.
Liberal MPs will thrash out their differences at a meeting on Monday afternoon, ahead of a joint party room meeting with the Nationals on Tuesday.
It is understood the majority of Liberal MPs favour sticking with the plebiscite, with a growing number advocating a postal vote which would not require legislation.
The Senate will open on Tuesday with a statement from Senate President Stephen Parry and the government asking that former minister Matt Canavan be referred to the High Court to test whether he is eligible to sit.
His mother signed a form making him an "Italian resident abroad" a decade ago - something the senator only discovered during the break.
Section 44 of the constitution bans MPs from being dual citizens, but Senator Canavan has initial legal advice his lack of consent could save his job.
The Greens are expected to refer Larissa Waters and Scott Ludlam to the court, having resigned their Queensland and WA senate seats over dual citizenship.
It is also expected One Nation senator Malcolm Roberts will be referred to the court over his British links, or at least he'll provide the Senate with documents supporting his case to stay in parliament.
Also in the upper house, a group of SA senators will call for a national judicial inquiry into allegations of theft and corruption involving water in the Murray Darling river system.
The government is hopeful of making progress on media reform and changes to university funding, as well as three workplace relations bills.
The House of Representatives will also debate laws to strengthen requirements for citizenship, and a further tranche of company tax cuts.
Nick Xenophon is expected to sit down with crossbench colleagues to nut out amendments to media reform bills which would stem cuts to journalism jobs and protect local news coverage.
A deal struck by Senator Xenophon with the government on changes to the building code will come under scrutiny.
Labor will seek to disallow the ban on enterprise agreements having conditions that deal with the number of apprentices, local jobs and safety issues.
"The Liberal Government's return of the ABCC and implementation of the Building Code is simply part of their anti-worker, ideological agenda," says Labor workplace spokesman Brendan O'Connor.
A report of an inquiry into higher education legislation will be tabled on Tuesday, paving the way for debate.
Inquiry reports are also due on toll roads, the insurance industry and dairy production.