An independent Scotland would leave working people both north and south of the border "worse off", Ed Miliband has warned.
The Labour leader spoke out as he took his shadow cabinet team to Scotland - where voters will decide whether or not to stay in the UK in a referendum in less than five months time.
Labour's front bench team will meet in Glasgow's Emirates Arena as part of a two day campaign trip to Scotland to urge people to vote No to independence on September 18.
Mr Miliband, shadow Scottish secretary Margaret Curran and Scottish Labour leader Johann Lamont will also take part in a public meeting in Motherwell later in the day.
The Labour leader said he would be " campaigning with my shadow cabinet to keep Scotland in the United Kingdom".
He added: "I don't have a vote in September, but I care deeply about the decision people across Scotland will make, and that's why I wanted to bring my team to Scotland today.
"I want to rebuild our country in the cause of social justice, make the changes needed to tackle the cost-of-living crisis, and create a more successful economy that works for hardworking people here in Scotland and across the UK.
"But I don't believe you can serve the cause of social justice and that of narrow nationalism. There are people in every part of the UK who need decent jobs, a government that will stand up for them against powerful interests like the energy companies and an NHS that is there when we need it most."
With the Scottish Government having set out plans to cut corporation tax in an independent Scotland, the Labour leader warned: " If Scotland was to separate from the rest of the UK, our country would be in a race to the bottom with the Nationalists competing on lower tax rates for the top and lower wages or living standards for everyone else.
"That's why working people in the UK will be worse off without Scotland and working people in Scotland will be worse off without the UK."
He added: " I want Scotland to continue to have the best of both worlds - strength, security and social justice as part of the UK, alongside a strong Scottish Parliament with more devolved powers.
"That needs a Labour government. And that is what we are determined to deliver."
The visit by the shadow cabinet comes days after former prime minister Gordon Brown gave a speech in Glasgow on behalf of Better Together, the cross-party campaign to keep Scotland in the UK.
Ms Curran said: " This is a big week for Labour in Scotland. Earlier this week, Gordon Brown gave his five positive reasons for Scotland remaining part of the UK and showed how we can have the best of both worlds with a strong Scottish Parliament and the protection of being part of the United Kingdom.
"And today, members of the shadow cabinet will take our message to communities across Scotland. We will be saying loud and clear why Labour believes Scots shouldn't vote to leave the UK. The entire Labour Party across the UK is behind our campaign to make sure Scotland remains part of the United Kingdom."
But the SNP has urged Mr Miliband to use his trip to Scotland to state his support for the formula which is used to allocate government funding to different parts of the UK.
Nationalists fear changes to the Barnett formula could result in Scotland losing £4 billion from its budget, with S NP MSP Sandra White claiming such a move would have " absolutely devastating consequences for communities across Scotland already suffering under Westminster's austerity agenda".
She added: " In the event of a No vote, Westminster has more cuts coming down the line - and Labour's weak Devolution Commission proposals don't offer any real powers to prevent these cuts hitting vulnerable people in Scotland.
"Labour voters across the country want substantial new powers for the Scottish Parliament - and more and more they are coming to the conclusion that only a Yes vote can deliver the powers we need to create a more equal society.
"With a Yes vote we can avoid any further cuts to Scotland's budget and will have all the powers we need to make Scotland a fairer, more prosperous country - which shows why Scotland can, should and must be independent."