Australia's New South Wales (NSW) state government is in crisis due to internal fighting over a policy designed to protect koalas.
The National Party, which is the junior coalition partner, says it will no longer support government legislation due to its opposition to the policy.
But party leader Deputy Premier John Barilaro said: "We are not anti-koala."
He said his lawmakers would no longer sit with Premier Gladys Berejiklian's Liberal Party in the state parliament.
It effectively puts Ms Berejiklian in minority government until the situation is resolved. She said she would strip National Party ministers of their portfolios if they did not change their mind.
The dispute - dubbed a "koala war" by the Sydney Morning Herald - relates to the government's State Environmental Planning Policy (Sepp), which became law last December. It aims to better protect koala habitats.
In June an inquiry found koalas would be extinct in NSW by 2050 without urgent action. Last summer's bushfires killed or harmed three billion animals nationally, according to a recent estimate.
But Mr Barilaro argued the protection policy went too far by placing onerous conditions on property owners about how they managed their land.
"We think a Sepp like this is somehow a way to sanitise the regions, attack the property rights of landholders and do absolutely nothing to support koalas," he said.
He added: "The National Party stands for a thriving koala population. We actually want to see the population double. We are not anti-koala."
But Liberal Party politicians said the measures were necessary and supported by the community.
Federal Greens leader Adam Bandt tweeted the Nationals were "blowing up the NSW government because they want rogue landholders to be able to kill more koalas".
Some conservationists have argued the current policy does not do enough to protect the animals.
Ms Berejiklian said it was "not possible" for a minister to sit on the crossbench.
"If required, I will attend Government House tomorrow and swear in a new ministry," she said, giving Mr Barilaro a deadline of 9:00 Friday local time (23:00 GMT Thursday).