Patrick Harvie has urged the First Minister not to take his party’s votes for granted ahead of the Scottish budget.
The Scottish Greens co-leader warned John Swinney that his party had brought down an SNP budget before and could do so again.
The comment is in reference to the 2009 budget which the Green party – which had two MSPs at the time – blocked over a row about a £33m home insulation programme.
Alex Salmond, who died earlier this month in North Macedonia, was first minister at the time while Scotland’s current First Minister, John Swinney, was finance secretary.
Delivering his keynote speech to the party’s conference in Greenock, Harvie accused the Scottish Government of making a “sharp U-turn” on climate policies since the Greens left government.
The Bute House Agreement between the two parties ended earlier this year after the then-first minister, Humza Yousaf, kicked the junior party out of government.
Since then, the Scottish Government has halted some policies supported by the Greens, including nature restoration funding and a pilot that scrapped peak rail fares.
Speaking to Scottish Green members on Saturday, Harvie said reversing these “broken promises” would be a priority for his party in budget negotiations.
He said: “We’ve shown how we could make big savings by stopping tax breaks to wealthy landowners and enterprise grants to arms companies, and by bringing in more money to support our healthcare system through a public health levy on supermarkets.
“But these steps are only the start. Extra funds raised through tax or coming from the UK Government must go into reversing the broken promises made by the SNP Government since they ended the Bute House Agreement.”
Harvie said that would include reinstating the plan to roll out free school meals to all primary school children before 2026 and funding a programme to cut energy bills while reducing emissions from heating homes.
He added: “As Scottish Green MSPs, we have a responsibility to engage with the process in good faith, and with honesty.
“But, as the only party that ever brought down an SNP budget, as John Swinney knows to his cost, we need to be clear that they cannot take our votes for granted.”
The Scottish Greens co-leader also warned his MSPs “would not wave through” the Climate Change (Emissions Reduction Targets) (Scotland) Bill.
The legislation was introduced after ministers announced – while the Greens were in government – they had abandoned a target of reducing emissions by 75% by 2030.
Harvie accused the Scottish Government of “dithering” on climate change.
He said: “The first two Climate Change Acts were statements of high ambition. This third one will be an admission that, as Greens have long argued, Scotland is years behind where we should be.
“It is an admission that needs to be made; but making it demands an urgent acceleration of action here and now, not just promises of more plans to come.
“But what have we seen in the last six months from the now minority Scottish Government?
“Instead of accepting that missed targets demand accelerated action, they’ve chosen a sharp U-turn on much of the action that the Greens had been advancing.”
The Scottish Government has been approached for comment.
Follow STV News on WhatsApp
Scan the QR code on your mobile device for all the latest news from around the country