The Soil Association estimates that GM soya, maize and oilseed rape could have cost the US economy $12bn in farm subsidies, lower crop prices, loss of major export orders and product recalls.
The Scottish National Party's environment spokesman, Bruce Crawford, said the report was "environmental dynamite" and called for an immediate moratorium on GM crop trials in Scotland.
But at the same time, another report, from the National Centre for Food and Agricultural Policy in the USA (NCFAP), said the six GM crops in the marketplace there had improved farm income by $973m in 2001.
They had produced an extra 1.8 million tonnes of food and fibre on the same acreage, said NCFAP, and the use of pesticide had been reduced by 21,000 tonnes.
The Scottish Parliament's health committee is to hold an inquiry into the effect on humans of GM crops.
Referring to the Soil Association's report, Green Member of the Scottish Parliament Robin Harper said: "If the [Scottish] executive ignores this warning, Scottish farmers could suffer.
"It's time for the executive to take responsibility for the welfare of Scottish farming on its shoulders and not lamely follow what's going on in England."
Approval has been given for a final round of crop trials in Scotland this autumn.
The new planints at Daviot, Aberdeenshire, and Newport-on-Tay in Fife, will be conducted by biotech company Aventis, which last month admitted that rogue material had contaminated previous crop tests.