Scottish independence would put Britain at the mercy of corporations who would play nations against each other to drive down wages and working conditions, Labour leader Ed Miliband said.
Mr Miliband urged voters in the Labour stronghold of Motherwell, North Lanarkshire, to reject independence and the low tax policies of SNP leader Alex Salmond - who he said is being inadvertently led towards a Conservative agenda by the "race to the bottom logic of independence".
"The SNP tell you that the way to tackle social injustice is with independence," he said.
"I submit to you that that is wrong.
"A clue to what Alex Salmond's commitments are is his first commitment, which is not on the NHS or even the bedroom tax. It's a 3p cut in corporation tax for the large companies.
"How can that be the first commitment of somebody who claims to be a social democrat, who claims to be committed to social justice?
"It's because he knows that if you separate two countries which have hundreds of years of history you draw an international border.
"That produces companies who say: 'If you don't do what we say we'll move across the border. If you don't lower your tax rates, if you don't make your wages and conditions worse, if you raise wages and conditions, we're going to cross the border.'
"It's what I call a race to the bottom in wages, conditions, tax rates and all of that.
"Is a race to the bottom going to tackle the cost of living crisis that I talked about? Is it going to tackle inequality? It is not. It's going to make it worse.
"Part of my argument against the Tory Government in London is that they believe in a race to the bottom.
"(Prime Minister) David Cameron and (Chancellor) George Osborne believe that the way we will succeed as a country is by low wages, low skills, worse terms and conditions and making it easier to fire people.
"I'm not saying to you that Alex Salmond believes in his heart like they do in the race to the bottom, but he is being pushed into that by the logic of independence.
"The logic of independence takes you to two countries competing against each other where the companies have the power and the governments are at their mercy."
Mr Miliband faced probing questions from the audience of Labour supporters, fellow unionists, nationalists, undecided voters and local high school pupils who will vote for the first time in a major poll.
North Lanarkshire Labour councillor Kay Harmon said: "When are we going to get the positive side of staying together as a country?
"More and more all we're getting is: 'Oh my goodness, here's another depressing message from Gordon.'"
Long-term Labour voter Bill Wilson said: "How are we to disassociate ourselves from the Tories and the Lib Dems again when this debate is over when we know that a Yes vote will not only get rid of Trident but it will probably get rid of the Tories as well?"
Mr Miliband said: "My message is a message of hope. We are potentially one Christmas away from getting rid of the Tory government with a Labour government.
"The SNP are trying to convince voters to vote Yes by promoting the idea that the Tories are going to win the election.
"This is a beatable Tory government, and I intend to beat it.
"On the Trident question, I am in favour of the minimum deterrent that we need in the UK. I'm not for unilateral disarmament.
"I am for multilateral nuclear disarmament. I think it is important that we lead the world alongside the US and others to bring about the disarmament that we want to see."
On the Better Together alliance, he said: "It is right for the purposes of this campaign to say that parties that are committed to the UK should have an organisation.
"It means that there are a common set of questions that can be posed about the dangers of independence, and a united set of views of some of the virtues of devolution."
One high school student said: "As a Yes voter I have been heavily criticised within my school by my peers, and I have been mocked by some of my teachers which I can deal with.
"But do you think that the Scottish Government has scored a bit of an own goal in making 16 and 17-year-olds allowed to vote because so many of them are voting No?"
Donna Morris, a homelessness charity worker, said: "In a vote in November to abolish the bedroom tax, 47 Labour MPs were paired and didn't turn up.
"That is brought up with me quite regularly as an issue for people who think that our MPs don't actually care enough to go and vote.
"In February, the Scottish Parliament came up with extra money to abolish the bedroom tax in Scotland in all but name.
"People in both camps have said to me: 'That is making me want to vote Yes. If we can be in the Scottish Parliament and there is no place for the politicians to hide and they work together why would we not want that in Scotland?'"
Mr Miliband said: "I don't think it was a mistake to give 16 and 17-year-olds a vote in the referendum because I want to give 16 and 17-year-olds a vote in the general election as well. The fact that the majority seem to be tending towards No is a good thing.
"On the the bedroom tax, there are votes that take place all the time in the House of Commons and we want to abolish the bedroom tax as soon as we possibly can.
"We need a subsequent vote on the bedroom tax, we need the House of Lords and the House of Commons to do everything we can to get rid of it.
"But it is a clear pledge from me that is what we will do straight away when a Labour government is elected and there is no ifs, buts or complicated formulas."
Mr Miliband brought his shadow cabinet team to Scotland today to urge voters to vote no to independence and yes to a UK Labour government in 2015.
Earlier today, he said the Conservatives were not just "disliked" in Scotland, where the party only has one MP, but were also unpopular in parts of England, such as Newcastle and Manchester.
Mr Miliband also restated his party's position on the prospect of a shared formal currency union in the event of independence.
Asked if such a deal - favoured by the SNP - was ruled out under any circumstances, he replied: "Correct."
"All of the lessons from the eurozone are that, if we are going to have a currency union, we also need the kind of fiscal union that we have across the UK."
Labour's frontbench team met in Glasgow's Emirates Arena as part of a two-day campaign trip.
Mr Miliband, shadow Scottish secretary Margaret Curran and Scottish Labour leader Johann Lamont took part in the public meeting in Motherwell.
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.
Commenting on Mr Miliband's visit, First Minister Alex Salmond said: "Ed Miliband has zero credibility when he comes to Scotland to talk about social justice.
"He backs a No campaign which is being bankrolled by rich Tory donors and which is aimed at keeping Westminster's undemocratic grip on Scotland.
"Labour has abandoned its principles and its leadership by working hand in glove with the Tories and the Westminster establishment against Scotland taking its future into its own hands.
"That is why so many leading and respected Labour figures have said they will be voting Yes in September and are urging others to do so.
"And it is also why so many ordinary Labour voters are planning to vote Yes in the referendum, as the opinion polls increasingly show.
"A Yes vote will mean that we never again have to endure unpopular Westminster Tory governments that we didn't elect - and independence will mean Scotland always gets the governments we vote for, allowing us to take the action we want on issues like the bedroom tax, the living wage and zero hours contracts.
"Ed Miliband's pledges on zero hours contracts are fatally undermined by the fact Labour has voted to keep such contracts in place in Wales.
"Ed Miliband may also try to claim his campaigning in Scotland is part of a stepping stone strategy to deliver a Labour victory at Westminster - but he claimed the same thing in the 2011 Holyrood election campaign and that ended in unmitigated disaster for him and his party."