The Scottish Parliament is to formally reject the UK government’s draft Brexit deal in a vote on Wednesday afternoon.
SNP, Labour, Green and Lib Dem members at Holyrood will back a motion rejecting the proposals, as well as the prospect of leaving without any deal.
However, the parties have not come to a consensus on an alternative plan.
The vote will be held as MPs at Westminster continue to debate whether to accept the withdrawal plan agreed between the UK and EU.
Prime Minister Theresa May is facing a struggle to get the agreement through the Commons, with opposition being voiced across the political spectrum ahead of a “meaningful vote” on Tuesday of next week.
A majority of MPs must back the proposals if they are to come into force – but the result of Wednesday’s vote at Holyrood vote will not be legally binding on anyone.
The SNP, Labour, Greens and Lib Dems came together to pen an agreed motion ahead of the Holyrood debate, saying in a joint statement that it would demonstrate that the “overwhelming view” of MSPs was against the deal.
The motion states that both Mrs May’s plan and a no-deal Brexit would be “damaging for Scotland and the nations and regions of the UK as a whole”.
It concludes that the parliament should “recommend that they be rejected and that a better alternative be taken forward”.
However, each of the parties will argue for their own preferred alternative plan – while the Scottish Conservatives will vote against the motion, arguing that it is “needless”.
The Scottish government’s Brexit secretary, Mike Russell, said Holyrood had a “historic opportunity” to “come together and formally oppose both a ‘no deal’ option and the prime minister’s damaging Brexit deal”.
He said: “The UK government’s own analysis shows why the draft Brexit deal is unacceptable – it would make us poorer while extending uncertainty.
“Our first priority is staying in the EU, in line with the overwhelming vote in Scotland to remain, and we support another referendum on EU membership. Short of that, the least damaging option is to remain in the single market and customs union.
“I welcome the cooperation we have seen so far in the Scottish Parliament. We should now reach a consensus and oppose both the proposed draft Brexit deal and the suggestion a no deal Brexit is the only alternative.”
Scottish Conservative constitution spokesman Adam Tomkins said the SNP and the Greens were using the debate to “manufacture yet more grievance as part of their push for a second independence referendum”.
And he accused the Labour and Lib Dem leaders of being “Nicola Sturgeon’s little helpers”.
Mr Tomkins said: “The Scottish Conservatives are the only party committed to respecting the results of both referendums we have held in the last four years.
“That clear, democratic principle is one we will seek to uphold in the Scottish Parliament today, in defiance of the SNP’s games.”