SNP deputy leader Angus Robertson is to accuse the UK Government of running scared of a second independence referendum.
The party's leader in Westminster will also accuse the Conservatives of having a "desperate desire" to prevent anyone rejecting "hard Brexit".
It comes as Prime Minister Theresa May said it would it be "fundamentally unfair" to hold a second Scottish independence referendum in the next two years, as she prepares to outline plans for a more united UK.
Mr Robertson is expected to tell the SNP spring conference in Aberdeen that it is for the people of Scotland to decide the country's future.
While First Minister Nicola Sturgeon has outlined plans to stage a fresh vote on independence between autumn 2018 and spring 2019, Mrs May intervened on Thursday to say "now is not the time" for such a ballot.
On Friday, the Prime Minister will pledge to forge a "more united" nation as she begins the Brexit process.
Mrs May will stress that the break from Brussels will require "one United Kingdom, all pulling together to get the best outcome".