A former deputy leader of the SNP has warned "scaremongering" business leaders they face a "day of reckoning" if Scotland votes for independence.
Jim Sillars accused some of "subverting Scotland's democratic process" and called for oil firm BP to be nationalised after independence.
A number of banks and retail figures have made high-profile interventions in recent days.
The pro-UK campaign claimed the 'Yes' campaign's "mask had slipped".
Mr Sillars appeared beside Scottish First Minister Alex Salmond and his deputy Nicola Sturgeon at a pro-independence event earlier this week.
The two men are said to have fallen out 20 years ago, with Mr Sillars recently describing Mr Salmond's plans for a currency union after independence as "stupidity on stilts".
'Lies and distortions'
Speaking on the campaign trail in Edinburgh's Wester Hailes area from his Margo Mobile, named in memory of his late wife, Margo MacDonald MSP, Mr Sillars said oil giant BP would face nationalisation in an independent Scotland.
He said: "This referendum is about power, and when we get a 'Yes' majority we will use that power for a day of reckoning with BP and the banks.
"The heads of these companies are rich men, in cahoots with a rich English Tory Prime Minister, to keep Scotland's poor poorer through lies and distortions. The power they have now to subvert our democracy will come to an end with a 'Yes'.
"BP, in an independent Scotland, will need to learn the meaning of nationalisation, in part or in whole, as it has in other countries who have not been as soft as we have been forced to be.
"As for the bankers: your casino days, rescued by socialisation of your liabilities while you waltz off with the profits, will be over."
Mr Sillars added: "What kind of people do these companies think we are? They will find out."
'Fear and intimidation'
His comments were seized on as "threats" by campaigners for a "No" vote.
Speaking on behalf of the Better Together campaign, Labour MP Ian Davidson said: "The 'Yes' campaign's mask slipped today as Jim Sillars revealed their message for the final week of this campaign - vote 'Yes' or else.
"His words are a clear threat to anyone who points out the true costs of separation to the people of Scotland.
"The 'Yes' campaign has been a campaign of fear and intimidation from the start. Many people have been silenced. Now those who put their head above the parapet get pot shots from desperate nationalists."
Mr Davidson added: "We have seen the 'Yes' campaign's thugs on the street - now we see their thugs with microphones and press releases.
"Sillars stood shoulder to shoulder with Alex Salmond this week claiming to be positive. Now we see the real face of nationalism in all its ugliness."
A spokesman for the pro-independence Yes Scotland campaign said: "Jim is a passionate campaigner who is carrying on the work of his late wife Margo MacDonald, who dedicated her political life to achieving an independent Scotland and a fairer society.
"The current Scottish government's proposals for an independent Scotland are set out in great detail in the White Paper - including the job-creating powers Scotland so badly needs - and that is what people are voting for.
"In each and every election to an independent parliament, parties and individuals can put forward a manifesto of their choosing and the people will decide."