The SNP today revealed plans to take legal action over this week's televised debate between the UK party leaders.
The Nationalists are aiming to raise a £50,000 fighting fund over 48 hours to pay for the action at the Court of Session in Edinburgh.
The party is angry that leader Alex Salmond has been excluded from Thursday's BBC debate between Gordon Brown, David Cameron and Nick Clegg.
They intend to lodge papers with the court on Tuesday, seeking a review of the broadcaster's position to "ensure that Scottish interests are properly represented".
The proposed action would seek to ensure that the debate is broadcast in Scotland with the nation's political make-up "fairly" reflected - either by having SNP representation in the debate or through an agreement to have a further leaders' debate organised before polling day.
Unveiling the plans, Mr Salmond branded the BBC's current stance a "disgrace".
He said: "The decision by the BBC, who are meant to be Scotland's national broadcaster, paid for by our licence fees, not to have the country's political make-up properly represented next Thursday is a democratic disgrace.
"Everyone knows it is a stitch-up demanded by the London-based parties and meekly agreed to by the BBC.
"That's why the SNP are today launching a fighting fund to raise the money needed to challenge the BBC's decision in court.
"We are mounting an appeal to raise £50,000 by midnight on Monday. That's the money we estimate we need to mount an action at the Court of Session in Edinburgh.
"It is a huge sum for a party like the SNP. But the issues at stake are too important to ignore."
Leaders' debates have already been held on ITV and Sky, with the final exchange set to be hosted by the BBC in Birmingham on April 29.
Liberal Democrat leader Nick Clegg has seen a notable rise in the polls since his appearance in the fist two shows.
The SNP's legal bid comes just days after the BBC Trust rejected appeals by them and Plaid Cymru in Wales against their exclusion from the debate.
Mr Salmond told the BBC's The Andrew Marr Show that he was not arguing for the final leaders' debate to be blocked.
"We're arguing for the debate to be screened, we're enthusiastic about the debate, we just want the debate to be fair and balanced," he told the programme.
He called for an extra debate, or for the SNP and Plaid Cymru to get the chance to put across their views during a section of Thursday's debate.
Mr Salmond said: "We're now in a situation where the most likely result in this election is a balanced or hung parliament.
"Don't you think that viewers across these islands might wish to know what the SNP and Plaid Cymru, who could be very important in that context, would do in that situation?"
He also dismissed suggestions that they should have mounted the legal bid before now, insisting all internal procedures had to be exhausted first.
He said: "We've been incredibly reasonable about this, we've tried to argue that there should be a further debate in which the SNP and Plaid Cymru should take part. We haven't asked for parity with the other parties, just to be included.
"But we have a situation where these debates haven't just dominated the election campaign, they've been the election campaign, so if you're excluded for them then that's extremely unfair."
Mr Salmond has now written to the chairman of the trust, Sir Michael Lyons, saying the BBC, as a national broadcaster for Scotland, has a special responsibility for impartiality and fairness, which it has now "abdicated".
He wrote: "It is deeply unfortunate that the actions of the BBC Executive and the trust have left us with no option but now to refer this matter to the courts.
"It is an extraordinary injustice that despite the repeated efforts of the SNP to ensure these debates not only take place, but take place on a fair basis, the BBC has not only failed to enter into discussions with the SNP on even terms as the other three parties but has failed to justify its decision to do so."
He added that the leaders' debates were "dominating" the General Election campaign.
"The news agenda of the BBC's own election output has revolved around these debates," he said.
"It is no longer credible for any broadcasting organisation to deny the impact these debates have had on the balance of election campaign coverage across all media."
If the Nationalists' financial appeal is successful, the party plans to lodge papers at the Court of Session first thing on Tuesday morning, the same day the SNP and Plaid Cymru say they should have been granted a hearing by the BBC Trust.Reuse content