Nicola Sturgeon is to accuse the UK Government of using Brexit to launch an "attack on the very foundations" of devolution.
Scotland's First Minister will warn the powers of the Scottish Parliament are at risk from the Conservative Government at Westminster following the vote to leave the European Union.
In an address to the David Hume Institute in Edinburgh, Ms Sturgeon will say that after 20 years of progress, devolution now faces a "grave threat".
Citing the majority vote in Scotland to remain in the EU and efforts to reach a compromise with the UK Government on Scotland's future place in Europe, she is expected to say: "The democratic deficit which fuelled the demand for a Scottish Parliament in the 1980s and 1990s has opened up again.
"The Brexit process has emboldened a now powerful Westminster faction, which never accepted devolution, and which now sees it as an opportunity to rein in the Scottish Parliament.
"In place of a multinational United Kingdom democracy, they see Brexit as the way to claw back ground."
Ms Sturgeon will say that despite promises made by the Leave campaign during the referendum that Holyrood would gain new powers repatriated from Brussels, statements suggest elements of farming and fishing policy "now risk being taken back to Westminster".
She will say: "That would be utterly unacceptable. It would be a gross betrayal of the claims and promises made during the EU referendum campaign.
"And more profoundly it would fundamentally undermine the basis of the existing devolution settlement.
"So what we have is in effect an attack on the very foundations of the devolved parliament we voted for 20 years ago.
"It is being made by a UK Government which speaks the language of partnership but which in reality pays scant if any heed to Scotland's democratic voice."
Ms Sturgeon has said a second referendum on Scottish independence would be the result of ''sheer intransigence'' on the part of the UK Government, and that her party has a ''cast-iron mandate'' to call another vote, justified by both the EU referendum result and the SNP's victory in last May's Holyrood election.
She will add: "The UK Government still has an opportunity to change course before it triggers the Article 50 process. I very much hope it does.
"However if it doesn't, it will show that the democratic deficit which people voted to end in 1997 doesn't just endure - it continues to cause harm to Scotland's interests, to our international relationships, to our very sense of our own identity.
"And so if those circumstances arise, proposing a further decision on independence wouldn't simply be legitimate, it would almost be a necessary way of giving the people of Scotland a say in our own future direction.
"It would offer Scotland a proper choice on whether or not to be part of a post Brexit UK - a UK that is undoubtedly on a fundamentally different path today than that envisaged in 2014.
"And in the absence of compromise from the UK Government, it may offer the only way in which our voice can be heard, our interests protected, and our values upheld."
Scottish Conservative leader Ruth Davidson said: "The UK Government's white paper on Brexit makes it very clear that no decisions currently taken by devolved administrations will be removed and that when powers are returned from Brussels, more decisions will be devolved.
"This hyperbole from the First Minister takes synthetic grievance to a whole new level. Frankly, she sounds shrill.
"Nicola Sturgeon's attempt to use Brexit to manufacture the case for a second referendum has quite simply failed.
"She should now take it off the table so Scotland and the UK can work to get the best Brexit deal possible."
Scottish Labour leader Kezia Dugdale said: "This is ridiculous scaremongering from Nicola Sturgeon.
"The Scottish Parliament has major new powers over tax and welfare, which the SNP simply refuses to use. Rather than claiming there is a 'grave threat' to devolution, Nicola Sturgeon could instead use the powers at her disposal to introduce a 50p top rate of income tax or increase child benefit, rather than picking yet another constitutional fight.
"It is a dereliction of duty for the First Minister to give up on devolution so easily. While the Tories' reckless Brexit gamble will undoubtedly harm Scotland's economy, there is an opportunity to repatriate powers here from Brussels - including fishing and agriculture."
A UK Government spokesman said: "These claims completely misrepresent the UK Government's position.
"We have been very clear that no decisions currently taken by Holyrood will be taken away.
"We have also said that we will use the opportunity of bringing decision-making back to the UK to ensure that more decisions are devolved.
"As a result of the Scotland Act passed last year, Holyrood is becoming one of the most powerful devolved parliaments in the world.
"The only threat to devolution is the policy of taking Scotland out of the United Kingdom."