The EPBC Act has emerged as a key test, with the government hoping to score a political milestone while the Liberal leader needs to prove her authority.
The final sitting week of federal parliament before the summer break is not usually the most edifying example of democracy in action. Politicians and the media are spent and the sausage-making process can get a little rough.
So it was at the end of 2024, as Labor moved to clear the decks with an election looming and rumours of a summer campaign spreading. On the last sitting day alone, more than 30 bills went through the Senate, including reforms to the Reserve Bank - and Labor's landmark social media ban for under-16s, now just weeks away.
But one major priority was thrown overboard. A deal negotiated with the Greens on environmental law reforms was junked by Anthony Albanese, after the WA premier, Roger Cook, warned it was a political stink bomb in Western Australia.
Fast forward 12 months - with Labor re-elected in a canter and the Coalition left demoralised - and the environment minister, Murray Watt, has crafted a new set of changes to the Environment Protection and Biodiversity Conservation (EPBC) Act, with their fate emerging as a key test for Canberra's final week.
For Sussan Ley - who is determined to hang on as opposition leader into 2026 - helping Labor get the plan over the line before Thursday night looks like a test of both credibility and authority.
It is one she can't afford to fail.
Watt has been clear for weeks that he intends to make a deal before Christmas, and he is prepared to negotiate with either the Coalition or the Greens. Business wants a deal done, even as environmental campaigners warn the legislation risks making the failings of the current Howard-era environment laws worse. The bill's "nature positive" moniker is long gone.
Seeking to secure her position after the Coalition's monumental backflip on support for net zero carbon emissions by 2050, Ley enters the final sitting days endangered, but likely not at imminent risk of a challenge.
On Friday, she went public with an offer to Labor to pass the EPBC bill provided the government agreed to fix seven points of concern, including the powers of the proposed environment protection agency; a requirement for large projects to disclose projected emissions upfront; and financial penalties.
If Labor agrees to the conditions and makes a deal sometime around next Wednesday night, the bill would pass in time for a victory lap from the prime minister and his problem-solving minister. Albanese already has a list of post-election achievements ready for touting.
For Ley, such a deal could reassert her authority over the divided Coalition joint party room and put outspoken Nationals - including Matt Canavan and Barnaby Joyce - in their place. Despite the opposition adopting his anti-net zero plan holus-bolus, Joyce is widely expected to defect to hard-right minor party One Nation, while Canavan has goaded Labor to make a deal with the Greens and suffer the political consequences.
Liberal sources told Guardian Australia some Coalition conservatives are more open to a compromise on EPBC reform, in part to avoid further distancing the party from their traditional allies in corporate Australia who support more ambitious policies like net zero.
Many business figures agree with authoritative former Treasury boss Ken Henry that EPBC reform is badly overdue and represents an opportunity to boost productivity in the economy.
But there's also the risk that negotiations with Labor lead to another implosion within the Coalition.
Ley needs that kind of breakdown with conservatives like a hole in the head.
For their part, the Greens say any deal done with the Coalition would badly lack credibility, given the party has abandoned real efforts to address carbon emissions. Leader Larissa Waters said on Friday the government's expedited timeline was suspicious, insisting meaningful reform need not be rushed.
The minor party's demands include an end to native forest logging and measures to consider the climate impact of projects as part of approvals. But sitting out a deal could marginalise the Greens and give Labor fresh ammunition to argue that the party of the environment has sought to stand in the way of environmental protections.
Ley faces a choppy final sitting week, even if, as expected, her rumoured leadership rivals Angus Taylor and Andrew Hastie hold off launching any challenge until sometime in 2026.
Monday's Newspoll in The Australian will set atmospherics for the week, the same day columnist and author Niki Savva releases her latest book, Earthquake, about the former opposition leader Peter Dutton's crushing loss at the May election.
Savva has a habit of making trouble for the Liberals, and Albanese is among her biggest fans. Copies of the book were spotted around Parliament House on Friday. Another Dutton critic, the former prime minister Malcolm Turnbull, will be on the scene next week as well, part of an event on national security planned with the teal independent Monique Ryan in Melbourne.
Ley has blitzed TV and radio since the net zero decision, delivering a major speech on defence, in which she pledged to improve the country's energy sovereignty, to boost intelligence ties and provide protection ahead of the arrival of Aukus nuclear submarines.
She also moved to take control of internal debate about immigration policy, deploying shadow ministers Jonathon Duniam and Paul Scarr to unite the party and avoid another high-stakes party room debate.
The opposition leader even had some clear air from her rivals in recent days, with Hastie keeping a low profile and Taylor travelling to Washington DC. On Friday though, Taylor turned heads with a slick social media post that looked a lot like a pitch for the leadership. He posted a Daily Telegraph video of him talking about aspiration, small business and Australians wanting to "stand in front of a single flag".
It's rare that a single political issue emerges as a test for leaders of Labor, the Greens and the Coalition all at the same time. If EPBC reforms go through on the government's timeline, a long overdue political milestone will have been reached.
Just whose standing is improved, and whose is weakened, will cap an amazing year in politics.