The SDLP leader Margaret Ritchie has said the 'lazy and unimaginative' draft budget must be improved before her party can support it.
The SDLP's formal response has warned the plan, meant to save £4bn by the end of 2014-15, could cost 9,000 jobs.
Mrs Ritchie's comments come amid tensions over the proposals, with the UUP also questioning its merits.
Sinn Fein and the DUP are backing the budget and accusing the SDLP and UUP of undermining the executive from within.
The UUP has refused to say whether it will back the budget at the final vote in March, with the party's health minister insisting he needs another £200m to be able to maintain current levels of service.
The period for public consultation on the budget closed last week, with more than 4,000 responses.
The SDLP's response to the consultation says that while other parties have claimed the plan could generate additional revenue of £1.6bn, it has only been able to identify £252m from the proposed methods.
'Never a pup's chance'
Mrs Ritchie said the budget was indistinguishable from what a direct rule administration would have implemented.
"We are absolutely duty-bound to use the budget, our only real economic lever, to rebalance and stimulate the economy with a focus on job creation," she said.
"I don't believe there has been any real effort to do this.
"The SDLP's opposition to this budget is not driven by antagonism to DUP and Sinn Fein - although it seems they are now lashing out at anyone who questions it.
"We believe that SDLP proposals for new revenue streams, capital receipts and cash-releasing efficiency savings, can indeed make the budget so much better."
BBC NI Political Editor Mark Devenport said First Minister Peter Robinson has warned the Ulster Unionists and SDLP that their ministers should not expect to be bailed out at the expense of their colleagues.
"Mr Robinson said that for electoral reasons, there was never a pup's chance of the UUP and SDLP backing the draft budget," our correspondent added.