Scottish Greens co-leader Patrick Harvie has said he "does not know" if his party will stay in government with the SNP.
Green members are to vote on whether to end a power-sharing deal with the SNP after it scrapped key climate change targets.
Mr Harvie told BBC Scotland it would be his preference to remain in government where the party could achieve more.
The Greens are to hold an extraordinary general meeting to decide the issue.
The BBC understands it is expected to hear a single motion on "whether the party continues to co-operate with the Scottish Government or not".
First Minister Humza Yousaf has said he values the power-sharing deal - known as the Bute House agreement, - and does not expect it to be scrapped.
He reiterated his support for the agreement before a pro-independence march in Glasgow on Saturday where he was joined by Greens MSP Ross Greer.
Mr Harvie told BBC Scotland's The Sunday Show he shared the anger of his party members over the fact that reducing greenhouse gas emissions by 75% by 2030 - which has been scrapped - was unachievable. The long-term target of achieving net zero by 2045 remains.
"It's been clear for a long time now that Scotland is not on track to meet that target," Mr Harvie told the programme.
"The truth is that while, for a long time, some people have been happy to describe Scotland as a world leader, or have self-congratulatory speeches about setting targets, we are years behind where we should be on taking the actions to reduce emissions."
He said there had been times when the Greens had been arguing for transformational changes and other parties that had voted for the targets voted against those changes.
"This is a moment that's critical for the future of climate policy in Scotland and critical to the future of our party," he said.
"Over the next few weeks we have probably the most important decision to make that we've ever had to make about the future of our party.
"My worry is that if we walked away at this point, we would decelerate climate action."
Mr Harvie said he did not know whether the Greens would remain in government - where he and fellow Greens co-leader Lorna Slater have cabinet posts.