The FDA (Food and Drug Administration) has certain regulations in place concerning GMOs. Any food tampered with in any way on a DNA level can be considered GMOs, and all GMOs are subject to review by the FDA. However, it is the company themselves who reports on the GMO-status of the foods, not the FDA. If the FDA finds that any substance that is GMO was not reported as such, criminal charges can be brought on the manufacturer. The rules are looser when it comes to food additives. Congress defined food additives as 1. Any substance the intended use of which results in its becoming a component of food, and 2. Excludes from the definition of food additive substances that are GRAS (Generally Recognized as Safe). GRAS can include natural and chemical additives and can be marketed without having been formally reviewed by the FDA. Again, the manufactures themselves determine whether or not their substance can be considered GRAS. And, again, if the FDA finds that the substances that the manufacturer labeled as GRAS is, in fact, not, then the distribution of the food can be stopped and criminal charges can be brought on. Even though the regulations for GMOs are strict, and testing is excessive, there is room for manufactures to use a GMO as an ingredient in a food, label it as GRAS, and avoid the FDA review (source).