Scottish Greens have set out their Budget red lines ahead of crucial negotiations with Finance Secretary Derek Mackay.
With the SNP no longer having a majority at Holyrood, ministers will have to seek the support of other parties if tax and spending plans for 2018-19 are to be approved.
The six Green MSPs, who backed the Government in the budget vote last year, are seen as the most likely candidates for this.
But as the draft Budget for 2018-19 continues through the Scottish Parliament, Green co-convener Patrick Harvie has made clear there are three key tests Mr Mackay will have to meet to win his party's backing.
The Green MSP said: "If the Government come back before January 31 with a revised budget that does not meet these three tests, we will be unable to give our support.
"The investment we seek will deliver a fairer, greener Scotland, and ministers know these are the right choices to make."
Scottish Greens insist they will not vote for the Budget if it cuts local government spending, citing analysis by the Scottish Parliament Information Centre (Spice) as showing councils could be left £157 million worse off.
Public sector pay is another priority area where the Greens want the Scottish Government to commit more cash.
In his draft Budget Mr Mackay set out that only those workers earning under £30,000 would receive a 3% wage rise, while higher earners would get a lower rise which the Greens said amounted to a "real terms pay cut".
Meanwhile council workers will not automatically benefit from the Scottish Government's new public pay policy, with local government having to fund any increases staff receive.
The third key demand is for more investment to help tackle climate change, with Greens urging that low carbon projects receive greater spending.
It comes after the SNP and the Greens voted together at Holyrood to pass a motion calling for the Budget to "protect public services, fund a fair pay increase for public sector workers and invest in low-carbon infrastructure".
Mr Harvie said: "The ball is in the Scottish Government's court. We have made very clear over recent months what our priorities are and where their draft budget is lacking, and SNP ministers and backbenchers were last week left with no option but to acknowledge this by supporting our position in Parliament.
"The investment we seek is to protect schools and other local services, help frontline staff doing vital jobs to catch up after years of erosion in their pay packets, and it's about building the new rail lines, better buses and affordable housing that Scotland desperately needs."
The Scottish Government wants to use its Budget to raise extra cash, with changes proposed for income tax in Scotland.
But under the current proposals while Scots earning between £33,000 and £43,000 will pay more, workers on between £43,000 and £58,000 will actually pay less than in 2017-18.
Mr Harvie branded this "absurd" saying his party had given ministers a range of proposals for raising additional revenue "most obviously by fixing the absurd anomaly in the proposed income tax system which cuts tax for people on high incomes".
A spokesman for Mr Mackay said: "The SNP Government's budget has been well received, with support for our proposals to deliver fairer taxation, invest over £400m of new spending in the NHS, support new investment in education and the low carbon economy, and to ensure that workers in our NHS and other parts of the public sector receive a pay rise - whilst dealing with continued cuts to Scotland's budget from the Tory government.
"The Greens have set out their proposals, and any other party interested in serious negotiations is welcome to do the same."