Former prime minister Gordon Brown and Scottish Labour leader Jim Murphy have pledged stronger welfare powers for Scotland.
They said their plan would build upon the "the vow" which was signed by the main unionist parties two days before the Scottish independence referendum.
Mr Brown told a gathering in Edinburgh it was now time to present more "radical change" in the "vow plus".
However, the SNP said the announcement was a "panic" measure by Labour,
The Scottish Conservatives said it was evidence of a Labour Party heading back to the "bad old days of high tax and high spending" and the Scottish Lib Dems said there "wasn't much new" in the proposal.
In front of Labour activists, Mr Murphy detailed his party's plan, which included;
- Clearer powers to vary social security benefits
- Wider responsibilities for tackling unemployment
- Devolution of the £1.8bn housing benefits system
- And devolution of power to local communities from Holyrood and Westminster
He claimed these would go further than the cross-party promises for Scotland.
By political editor Brian Taylor
During the referendum, Labour - and Gordon Brown, in particular - laid enormous stress upon the danger, as they saw it, of breaching the shared benefits structure of the United Kingdom.
To be fair, they are still doing so. But the underlying emphasis has changed.
Gordon Brown now talks of UK provision as a baseline, as a minimum. He talks of the Scottish Parliament topping up benefits - with the final say allocated to Holyrood. By contrast, it would not be feasible for Holyrood to cut benefits: the UK baseline would kick in.
There would also be the power to create new benefits, the full devolution of Housing Benefit (uncoupled from Universal Credit) and the transfer to local authorities of the Work Programme.
After May's general election, Holyrood is due to receive more powers over income tax; a proportion of VAT raised in Scotland would stay in the country and air passenger duty would be fully devolved.
The Smith plan, detailed in a command paper which was published at the end of January, said the Scottish Parliament would be able to create new benefits but UK-wide welfare systems such as Universal Credit would remain under Westminster control.
Mr Murphy said delivering the vow was a starting point, not an end point for Scottish Labour.
He told the gathering: "We won't just deliver the vow, I want to confirm today that we will go further.
"Delivering the vow is an important point but not an end point for Scottish Labour.
"Only Labour can offer the change that people want to see: the ability with Home Rule to make distinctively Scottish decisions.
"And the power to redistribute the wealth of the UK to invest in our NHS and to give young people more job opportunities."
Mr Brown said that the Scottish Parliament should have the "final say" over benefit levels in Scotland.
He added: "The vow was a landmark in decades of devolution debate. It represented the overwhelming desire for change expressed by the Scottish people.
"It encapsulated our demand for a stronger Scottish Parliament. It showed a determination that Scotland should move forward in a new way and with faster, safer and - we believed - fairer change than proposed by the SNP.
"It showed that the choice in the referendum was not between the status quo and independence but between two visions of Scotland's future: change within the UK as against change by leaving it."
He added: "And so we are breaking with the Conservatives and Liberal Democrats whose weaker version does not go far enough and we are putting forward the stronger version.
"It is in fact the 'vow plus' - further radical change."
However, the SNP's deputy leader Stewart Hosie said the move by Mr Murphy and Mr Brown was evidence of "sheer panic" caused by Labour's poor poll ratings.
He added: "Labour are under severe pressure from the people of Scotland, who are backing the SNP in increased numbers.
"And if this is what Labour do when faced with disastrous opinion polls, Scotland will be able to achieve so much more by electing a strong team of SNP MPs to hold the balance of power at Westminster.
"Last month, Labour tried to tell people that the Vow had been delivered and there should be no more discussion of further powers for Scotland.
"Today, as more and more people back the SNP ahead of the coming election, Labour have been dragged along in Scotland's wake."
Scottish Tory leader Ruth Davidson said most Scots understood that it was better to have a job than to be "parked on welfare under the state".
She added: "Gordon Brown is yanking the Labour Party back to the bad old days of high tax, high spending and high borrowing that crashed the economy in the first place.
"The SNP wants to rip Scotland out of the Barnett formula, making our schools and hospitals rely on falling oil revenues.
"Only the Scottish Conservatives believe in balancing the economy, sharing resources right across the UK and getting people back into work."
Scottish Lib Dem leader Willie Rennie said that Labour "seem to be making it up as they go along".
He added: "In the Smith Commission they were the most cautious on transferring welfare powers to the Scottish Parliament.
"We had to work hard to convince them of the merit of creating a £3bn Scottish welfare system.
"Within weeks of agreeing this radical package they now claim it's not enough. The reality is that there is not much new in their proposals."