Large retailers immediately slammed the additional squeeze on their costs as "alarming" as they maintained their threats of legal action against the move, which they claim is unfairly targeting just one sector of the economy.
The so-called supermarket tax was announced last month as part of Swinney's 28 billion one-year spending plan following a cut in Scotland's budget for 2011-2012.
The Scottish Government is yet to announce the full details of the scheme, but the extra revenue will be raised through retailers' business rates.
Swinney put a figure on how much he hoped to raise from the move for the first time last week in a hearing before the Local Government and Communities Committee. He said larger retailers could easily absorb the rise in their cost base given that they continue to generate robust profits.
"I would expect to raise about 30m," he said. "I think it can be sustained by a sector that is performing well despite the economic difficulties we are facing."
David Lonsdale, assistant director at CBI Scotland, said of the sum: "The Scottish Government's decision to levy a business rates surcharge on larger retailers and out-of-town retail parks is alarming.
"The devolved administration should be making it easier for retailers to invest and create jobs here in Scotland, not more expensive.
"It is unclear why retailers have been singled out for higher taxes, or indeed whether we may see in future Budgets other sectors being similarly targeted."
Fiona Moriarty, director of the Scottish Retail Consortium, repeated her threat of legal action if details to be published shortly prove retailers' suspicions that they are being unfairly singled out.
Retailers already account for a quarter of the Scottish Government's business rate intake, according to the consortium - the highest proportion of any economic sector.
"Our members still continue to be extremely concerned about the proposed changes," Moriarty said. "It's the one sector in the Scottish economy that continues to grow and offer new job opportunities.
"This substantial extra financial burden is coming at a very bad time for retailers.
"When we see the detail we'll spend time analysing it and if we feel it is justified, we'll mount a legal challenge."
Retailers have warned that the additional burden could derail store opening plans which would in turn starve the Scottish economy of much-needed jobs.
It is believed that retailers could throw the European law book at Swinney, which dictates that firms can't be discriminated against by size. But the Finance Minister said: "It's a cost that is very much at the periphery of the cost base of these organisations."