Scotland's opposition leaders have joined forces against the government's proposals for a ballot on independence.
Labour, the Conservatives and the Liberal Democrats said they would block the plans, to be set out in a white paper due to be published on Tuesday.
They claimed that the Nationalists were pursuing a failed agenda that would damage Scotland.
A government spokesman suggested the parties may have "misunderstood" the nature of the document.
Labour, the Tories and the Lib Dems moved to oppose the white paper a day before it is expected to be published.
Without their support in the Scottish Parliament, the minority SNP government would struggle to get its plans through.
But the SNP has been at pains to depict the promised debate as a "national conversation" to give a voice to those seeking independence as well as people who support more powers for the Scottish Parliament.
The three opposition parties, which will now jointly review the devolution settlement, opening the prospect of Holyrood gaining additional powers, made known their concerns in a strongly-worded joint statement.
"The SNP is squandering taxpayers' money in pursuit of their own narrow and failed agenda," it said.
"They have promised to build a consensus around the policies they will bring forward for debate in the Scottish Parliament. But this white paper can only create division and uncertainty which will damage Scotland."
The statement continued: "The SNP have spoken about a national conversation but tomorrow's publication is about their nationalist crusade.
"We will listen, but we fear this will be less of a conversation than a one-way megaphone.
"We are deeply concerned that the proposals to be made by the SNP are only designed to drag the people of Scotland into a constitutional cul-de-sac.
"We will not give succour to those who want to end the Union."
A Scottish Executive spokesman suggested the opposition parties might be unclear about the nature of the white paper.
He said: "To some extent the opposition parties have misunderstood the nature of the document tomorrow which is a broad and inclusive document where clearly the government sets out its views about the best way forward and the best way to get that, but is very open to other voices and other views.
"Even before the document is published, the other parties are, collectively or individually, finding it impossible to ignore this process."