SNP MPs at Westminster could "vigorously and loudly" support a Labour government in some areas, Nicola Sturgeon has said.
While the Scottish First Minister hit out at Ed Miliband's party for being "determined to continue with a failing cuts agenda", she stressed there were "many" issues where they could find common cause.
She highlighted their opposition to zero hours contracts and a shared desire to increase the national minimum wage as areas where the SNP could support a future Labour government.
Ms Sturgeon spoke out as she addressed the Scottish Trades Union Congress annual meeting in Ayr.
She told activists there: "I know Ed Miliband addressed you yesterday, and let me say in some areas like improved working conditions, a determination to crack down on zero hours contracts and increasing the minimum wage - though I would like to go further than he would to £8.70 by 2020 - on these and many other areas we have similar views.
"Where we support proposals a Labour government would put forward we will support them vigorously and loudly."
With the polls pointing to the May 7 election resulting in another hung parliament, Ms Sturgeon - whose SNP is tipped to return a record number of MPs - could hold the balance of power across the UK.
Any deal between the Conservatives and the Scottish nationalists has already been firmly ruled out by both parties.
But while Mr Miliband has said he will not go into formal coalition with the SNP, he has not ruled out working with Ms Sturgeon's party on an issue-by-issue basis to win the support he needs.
Ms Sturgeon said she would use whatever influence she has to make a future Labour government "better, bolder and more radical".
She stated: "It does sadden me that Labour seem determined to continue with a failing cuts agenda - not because it's necessary but because they want to be seen as tough as the Tories. I think that is the wrong approach. The Tory policy of austerity and cuts have failed and when a policy is failing you don't continue it, you decide to change it and put in its place something better.
"The SNP will never, ever, ever in a month of Sundays support a Tory government but we will use our influence, if the Scottish people choose to give us that influence, to make sure the Tories are replaced not by a Tory-lite government but by something that is better, bolder, and more radical.
"We need to get rid of the Tories but we need to replace the Tories with a government that won't simply implement Tory policies
"If there is a big group of SNP MPs at Westminster we will use that influence to strengthen Scotland's voice."
She added: "In this election I believe it is important that we have a voice that is shouting for an alternative to austerity. That is what I and my party will continue to do.
"Instead of the continued cuts agenda, we propose sensible, moderate increases to public spending while still reducing the deficit as a share of income in every year."
Ms Sturgeon said her party's plans to raise the minimum wage to £8.70 an hour by 2020 would leave 250,000 people in Scotland better off, with some benefiting by as much as £4,000 a year.
She argued: "Hard-working people have been let down by Westminster - with the cost of living rising as the harsh cuts agenda takes its toll.
"We need a new, progressive approach to tackle inequality, boosting pay for our lowest paid workers and helping close the gap between rich and poor.
"The SNP manifesto sets out a clear package of measures to stand up for working people. At the centre of this is a commitment to increasing the minimum wage to £8.70 an hour by 2020.
"This would build on the progress we have made by introducing the Living Wage - and make a quarter of a million people in Scotland better off by up to £4,000 a year."
Earlier, the First Minister said that if the UK voted to leave the European Union, that could justify a second independence referendum for Scotland.
Ms Sturgeon has refused to rule out staging a second independence vote after the 2016 Holyrood elections -but has said there would need to be some "'change of circumstances'' across the UK before this could take place.
In an interview with the Daily Mail, she said: ''I'm quite clear - a vote for the SNP at this election, I'm not taking that as a mandate for another referendum.
''So it would have to be something like the EU situation, if there was an Out vote across the UK and Scotland wants to stay in.''
She added: ''If I put a commitment to a referendum in any future SNP manifesto, people have to vote for that manifesto, so I can't do that lightly. I have to be sure that there is a change of circumstances that has led to people by majority opinion wanting another referendum.''
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