This move had been opposed by organic farmers and consumers because of the strong possibility that genetically modified alfalfa will cross-pollinate non-GM alfalfa. This has been recognized by the Supreme Court as potentially harmful to the organics sector, since organic foods cannot be produced with genetically modified crops. Once organic livestock are fed GM alfalfa, they can no longer be called organic.
— The Atlantic, Why You Should Care About Genetically Modified Alfalfa