In approving genetically engineered salmon as safe to eat and safe for the environment, the Food and Drug Administration rejected petitions from environmental and food safety groups asking that companies selling this salmon be required to label it as genetically engineered. Congress should overturn that decision. The salmon, made by AquaBounty Technologies of Maynard, Mass., has genes inserted that allow it to grow to market size twice as fast as wild salmon. At least one consumer group has announced plans to sue the F.D.A. to overturn its approval of the engineered salmon. Some leading grocery chains, responding to consumer concerns, have said they won't sell the genetically engineered salmon. The F.D.A. said there is no reason to mandate labeling because there is no material difference between engineered and natural fish. But the value of that information should be left to consumers to decide. Vermont enacted a law last year that will require labeling of genetically engineered foods starting next July unless a suit filed in June 2014 by four industry trade groups derails it. Other states with strong consumer movements may try to follow. The House passed a bill on July 23, 2015, that would pre-empt states from requiring such labeling, and industry groups are pressing the Senate to attach similar language as a rider to an omnibus spending bill. The Senate should rebuff that tactic and allow states to adopt mandatory labeling laws if they wish.