Campaigners say the $500,000 grant to AquaBounty amounts to a bail-out for the firm's main investor, the business tycoon and former economics minister of Georgia, Kakha Bendukidze. They are also comparing it to the Solyndra controversy, which saw a solar company go bankrupt after receiving government loan guarantees.
"Certainly this does have shades of Solyndra. We have seen this company's stock plummeting for months and months - years actually - and what does the US Department of Agriculture (USDA) do but give this company money?", said Colin O'Neil, a policy analyst at the Centre for Food Safety, which opposes GM salmon.
"This is research that any public university or independent institution could be doing, so why is the USDA funding this interested company to do it?" he said.
The grant, awarded last month, comes at a critical juncture for AquaBounty.
After $67m and 16 years' waiting, the Food and Drug Administration could pronounce GM salmon fit for human consumption within weeks, the company's chief executive, Ronald Stotish, said.
"Based on what we are seeing we believe we will have an approval by end of this year but we plan for all contingencies," he said.