Several U.S. grocery chains have agreed not to sell a genetically engineered salmon that is nearing approval from the Food and Drug Administration after 17 years of development, a group of environmental and consumer groups said Wednesday.

Retailers that have agreed not to sell the fish include national chains Whole Foods and Trader Joe’s, Aldi stores in the eastern half of the country, and PCC Natural Markets in Washington state. Most of the biggest supermarket chains are not participating.

Food activists who lost the battle over California’s Proposition 37, which would have required labeling of genetically engineered foods and was defeated in November after food companies spent millions of dollars to campaign against it, now are applying pressure via retailers. That is not a tough sell, because such foods poll poorly with the public.