Ed Miliband has accused the SNP of working for a Conservative victory in May's General Election.
The Labour leader levelled the accusation during a campaign event in Clydebank - where he arrived to more bad news from the opinion polls.
According to a new analysis by Scotland's leading polling expert, Professor John Curtice, his party could be left with just two MPs North of Border as the SNP capture 53 out 59 seats.
Mr Miliband used a speech to supporters to highlight differences between Labour, Conservative and SNP economic policies.
In a Q and A session after the speech, he was asked whether Mr Salmond - who talked up SNP hopes of a post-election deal with Labour at the weekend - had Labour "over a barrel".
The Labour leader said: "There seems to now be an unholy alliance between the Conservatives and the SNP to carry on a Tory Government.
"Frankly Alex Salmond is at it again."
He accused the former First Minister of "bluster and bluff," adding: "I gather he's got a book to sell."
Mr Miliband hit out after Mr Salmond said the SNP would support a minority Labour government on a vote by vote basis.
The Conservatives seized on his comments, issuing a new campaign advert saying Mr Salmond would "call the tune" if Mr Miliband became Prime Minister.
Mr Miliband went further than he has before in playing down the possibility of an informal power sharing deal with the SNP after the election.
He said: "I'll tell you who is going to be writing a Labour Budget, it's me and Ed Balls. Not Alex Salmond in a million years.
"It will be for other parties to decide how they vote on Labour's Queen's Speech."
In his speech, Mr Miliband said last week's Budget provided a "dramatic illustration" of the differences between Labour and Conservative economic plans.
He said only Labour could end the Tories' ideologically driven austerity programme.
He also hit out at the SNP's demand for devo max, which he claimed would leave Scotland £7.6billion worse off next year.
Shadow Foreign Secretary Douglas Alexander has previously accused the SNP of working for a Conservative victory, arguing the Nationalists would welcome David Cameron's return to Downing Street in the belief it would increase support for independence.
The new Guardian ICM poll put support for the SNP on 43 per cent and Labour on 27 per cent, virtually unchanged since December.
On a uniform swing, the SNP would win 43 seats to Labour's 12.
However, Professor Curtice said Labour could be reduced to two - holding Glasgow North East and winning East Dunbartonshire from the Lib Dems - as former Labour heartlands were turning to the SNP in bigger numbers than elsewhere.
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules hereComments are closed on this article