The leader of Better Together also said the No campaign was considering making a formal complaint to the Electoral Commission, the elections watchdog, over the allegations. "We are looking at all the options," he said.
One of the SNP figures at the centre of the row, Angus Robertson, has forcefully denied putting pressure on Gavin Hewitt, the former chief executive of the Scotch Whisky Association.
In a Dispatches programme for Channel 4 last night, Mr Hewitt claimed the SNP and its Westminster leader had regularly tried to urge the SWA to stay out of the referendum debate. He claimed Mr Robertson "was trying to neuter business comment".
"There was a genuine fear that if we were seen to scupper by coming out publicly against independence, there would be retribution down the track," said Mr Hewitt.
But Mr Robertson suggested the former chief executive was contradicting himself, pointing to a report last month in this newspaper when Mr Hewitt said the intimidation directed against him by the Nationalists had not been in the context of the independence referendum but added: "I do know people who have had calls in the context of the independence debate. But for obvious reasons I'm not going to indicate who. It does go on unfortunately."
Mr Robertson explained as the MP for Moray, representing more than half of Scotland's malt whisky distilleries, that he worked hard to promote the industry and had liaised with the SWA on industry regulation and taxation.
He said he had met Mr Hewitt on numerous occasions but had never had a private unaccompanied meeting with him, adding: "There is nothing in my conduct, which answers to Mr Hewitt's description."
But Mr Darling said the claims of bullying were "shining a light on Scotland that frankly brings shame on our country".
The former Labour Chancellor said when he first heard about the claims "over two years ago", he did not believe them but now so many people were speaking out.
"What worries me is that, if Scotland became independent, the same people doing these things would be in government. What sort of country would that be?
"If this was happening at Westminster, there would be an outcry. It strikes at the heart of the campaign. It should not be tolerated."
Elsewhere, Sir Menzies Campbell, the former Liberal Democrat leader, also claimed there was "a lot of bullying and intimidation" by the Nationalists.