Gavin Hewitt, the former British ambassador in Belgium, Finland and Croatia, said it was evidence that the nationalists tried to intimidate opponents into silence.
The former chief executive of the Scotch Whisky Association, said: “When I was putting together a list last August of businesses which disagreed with independence, we found about 150 people prepared to sign up.
“But almost as many refused because they feared they would be punished in terms of receiving grants, winning contracts or getting access to ministers.”
He added: “I know people in business who have experienced considerable pressure from the SNP. They were told in no uncertain terms by ministers that if they came out against independence, they should expect that existing contracts would not be renewed.”
However, a spokesman for finance secretary John Swinney dismissed Mr Hewitt’s claims.