The votes of Holyrood’s six Green MSPs were crucial in passing the SNP minority government’s Budget Bill last year and party members have now voted on a mandate for any potential future discussions.
At their annual conference in Edinburgh, members backed a motion calling for the “progressive use of newly devolved tax powers, to raise the revenue needed to protect public services and investment”.
The motion said: “Refusal by the Scottish Government to make further use of the powers available to it is unacceptable.”
Co-convener Patrick Harvie said: “Greens are leading the change in so many ways, but on income tax it’s our progressive proposals that have truly shifted the debate.
“With the powers Scotland has over rates and bands we can do so much more than simply tweak the basic rate, as some parties have suggested.
“We can instead cut tax for low earners, raise it for high earners, and altogether generate extra funds for public services.”
Mr Harvie said the party would not support the budget unless there is a real terms pay increase in line with inflation.
Speaking to BBC Sunday Politics Scotland, he said: “They have said they will lift the 1 per cent pay cap. That is not the same as a real terms increase. With inflation going up we really need to push the SNP much further than they’ve gone on this.
“Lifting the pay cap would still imply a below-inflation increase. That means a real terms pay cut.”
Asked if he would vote against the budget when it was pointed out that a real terms rise would by over 3 per cent, Mr Harvie said: “Yeah, and that’s the position that the trade unions are pushing as well.
“They are in negotiation on behalf of their members with the Scottish Government, but I want to support the basic principle that the people delivering our public services - services that every one of us depend on every day - deserve to have their wages protected rather than eroded even further.”
The Green conference also agreed that the EU Withdrawal Bill should be denied the legislative consent of the Scottish Parliament.
Members voted for a motion calling for the devolution of immigration and asylum powers to Holyrood.
External Affairs spokesman Ross Greer said: “The Tories’ hard Brexit disaster looms ever closer, and it’s right that as Greens we step up our fight to protect EU citizens who have made their home in Scotland, and that we send a message that Scotland remains a welcoming country.
“The Repeal Bill in its current form is utterly unacceptable. The UK Government needs to listen to Scotland, listen to EU citizens who live and work here and reform its approach urgently.
“In this form, the Repeal Bill cannot be passed and Green MSPs will withhold our legislative consent.”