MSPs are set to formally protest against changes to the UK benefits system, which some claim will see cuts in payments to the most vulnerable.
SNP and Labour members of the Scottish Parliament are expected to take the unprecedented step of voting against a Westminster “consent” motion.
Holyrood cannot stop Westminster changing the welfare benefits system.
But the UK government wanted Holyrood to allow it to change the law so its reforms would fit the Scottish system.
The UK government said the Welfare Reform Bill would save billions of pounds by replacing Disability Living Allowance with a personal independence payment and replacing a range of other benefits with a single universal credit.
But these changes will have a knock-on effect for devolved services such as social care and devolved entitlements such as free school meals.
MSPs are expected to turn down Westminster’s consent request in favour of making the necessary legal changes themselves.
It will be the first time Holyrood has refused Westminster legislative consent.
Scottish Health Secretary Nicola Sturgeon said the changes to welfare proposed by the Tory-Lib Dem coalition at Westminster would result in damaging cuts to benefits for some of the most vulnerable people in Scotland.
The UK government denied it was targeting the disabled and vulnerable.
It said the changes under the bill, due to come into effect in 2013, would save £7bn in welfare spending and encourage people currently on benefits to go out and find a job.
It has proposed moving to a single universal credit from 2013, to be paid to people both in and out of work.
The bill replaces child tax credit, working tax credit, housing benefit and income support, among others – but critics argue many in need of vital support will be worse off.
On Thursday, SNP and Labour MSPs will vote down part of the motion on the introduction of universal credit and personal independence payments.
The Scottish government will then need to bring forward its own legislation to ensure policies tied to the UK benefits system continue to operate in Scotland.
It is disappointing the Westminster government has not chosen to make changes to reflect the very real and deep concern expressed about the consequences of their proposals”
Martin SimeScottish Council of Voluntary Organisations
Ms Sturgeon said: “We recognise the welfare system is broken and needs to be fixed, but not at the expense of our most vulnerable people.
“Put simply, the Scottish government supports a welfare system that is simpler, makes work pay and lifts people out of poverty however this approach is being fundamentally undermined by the UK government’s deep and damaging cuts to benefits and services that will impact on some of the most vulnerable people in Scotland.
“We have put on the record time and time again our long-standing concerns about the lack of detail around key elements of the bill, which will have serious implications for devolved policies and services.”
A spokeswoman for the UK Department for Work and Pensions said: “We are pleased that the Scottish government recognises the welfare system needs urgent reform so it’s fair, simpler and that work always pays.
“These reforms will end the cycle of generations of Scots living a life on benefits whilst ensuring that those people who need our help and support get it unconditionally.
“When one in five Scottish households is workless, something fundamental needs to change.”
MSPs have previously heard concerns that the Welfare Reform Bill would increase pressure on homelessness and social care services and force disabled people to move home.
Children’s groups also claimed it could plunge between 50,000 to 100,000 youngsters into poverty.
Martin Sime, chief executive of the Scottish Council of Voluntary Organisations, said: “SCVO has always accepted that some welfare reform is necessary and welcome, but it is disappointing that the Westminster government has not chosen to make changes to reflect the very real and deep concern expressed about the consequences of their proposals for the most vulnerable members of our society.”
Bill Scott, of disability organisation Inclusion Scotland, added: “Even at this eleventh hour, we hope that the UK government might re-discover its conscience and halt reforms which will impoverish and severely limit the independence of tens of thousands of disabled people.”
Despite the opposition, MSPs are expected to support other aspects of the Welfare Reform Bill, under the legislative consent motion, including changes to data sharing, industrial injuries benefits and a new commission on social mobility and child poverty.
The Scottish Parliament is also likely to agree to creating a new committee dealing with the issue of welfare.