It follows a letter from CBI Scotland director Iain McMillan which appeared in yesterday's Scotsman attacking former merchant banker Ben Thomson, who now heads the centre-right think-tank Reform Scotland, over his support for full fiscal autonomy.
Mr Thomson had criticised Mr McMillan, in another letter to the paper, and his role in the Calman Commission, whose recommendations for limited new tax-raising and borrowing powers form the basis of reforms being brought forward by the UK government.
Speaking to The Scotsman, Mr McMillan also complained that the Campaign for Fiscal Responsibility, led by Mr Thomson, had "become very personal in its attacks".
Mr McMillan pointed out that the Calman Commission was backed by a majority of MSPs and the UK gGovernment, unlike the SNP government's National Conversation consultation on an independence referendum.
In the letter, he adds: "To argue, as Mr Thomson does, that the National Conversation has equivalence to Calman, and there has been no public consultation or debate, is plain ridiculous."
While praising his rival for being "a successful and talented businessman", Mr McMillan accuses him of being "obsessed with fiscal autonomy".
Responding to the attack, Mr Thomson said Mr McMillan's claims were "puzzling".
He also dismissed at any suggestion that he was politically motivated.
He said: "Reform Scotland, of which I am chairman, is an independent, non-aligned think-tank whose proposals over the past three years have been praised and adopted by a variety of political parties."