Legislation paving the way for a new referendum on Scottish independence is to be published at Holyrood.
Constitutional Relations Secretary Mike Russell will give a statement to MSPs on Wednesday afternoon on the “next steps on Scotland’s future”.
This will include details of the bill and of plans for a “citizens’ assembly” to discuss Brexit and independence.
First Minister Nicola Sturgeon has said she wants a new vote to be held in the second half of 2020.
However the “framework bill” will not set a date for such a referendum, with Ms Sturgeon committed to striking an agreement with the UK government before calling a vote.
The Scottish Conservatives said the “latest stunt” was “all about Nicola Sturgeon pandering to her party, not speaking for the country”.
Ms Sturgeon announced in April that she wanted a new independence referendum to happen before the end of the current Scottish Parliament term in 2021.
She told MSPs that she wants to secure a “Section 30 order” – an agreement similar to that underpinning the 2014 referendum – from the UK government before doing this, to put the vote “beyond doubt or challenge”.
The UK government has so far rejected such an agreement, but Ms Sturgeon said the government would bring forward legislation to “set the rules for any referendum that is now or in the future within the competence of the Scottish Parliament”.
She wants the legislation to be passed by the end of this year, with a view to applying it specifically to a second independence referendum in the event a deal is struck with UK ministers.
Speaking ahead of Wednesday’s statement, Ms Sturgeon said that “Scotland must have the chance to choose a better future than the one being offered by Westminster”.
She said: “The Westminster political system is broken and has shown it cannot be trusted to acknowledge, far less protect or defend, our national interests.
“People living here must have the opportunity to choose a future for Scotland as an equal, independent European nation.”
Holyrood’s pro-Union opposition parties hit out at the move.
Scottish Conservative constitution spokesman Adam Tomkins said it would “come as no surprise to anybody in Scotland that Nicola Sturgeon has decided to use the EU elections to manufacture the case for a second independence referendum”.
He said: “No matter what people in Scotland say or do, the SNP’s answer is always the same – to take us out of the UK.
“At a time when we need to focus on the challenges on education, the economy, and public services, this proves that the SNP has become a waste of parliamentary space.”
Scottish Lib Dem leader Willie Rennie added: “Not one patient will be seen quicker nor one school child get a better education as a result of Nicola Sturgeon’s independence obsession. All it will do is damage our economy and hurt our public services.”