The USDA regulation mandating identification of food ingredients with genetically modified organisms (GMOs) went into effect on New Year’s Day but is still plagued by uncertainty.

The regulation, called the National Bioengineered Food Disclosure Standard, requires food processors to inform consumers, in various ways, if a product contains GMOs. Although it technically went into effect on Jan. 1, mandatory compliance won’t be in place for another two years, and the USDA will depend on self-reporting for enforcement.

One of the challenges the regulation faces is determining just how foods that may contain GMOs can be exempted from the regulation. Many ingredients, like corn syrup or soybean oil, are made from commodities that are often bioengineered, but they undergo such extensive refining that their genetic material is destroyed. Foods made with such ingredients are exempt from having to declare themselves as bioengineered on that basis.

The USDA now has to decide how to apply these exemptions. It has issued a draft guideline for confirming that a refining process for ingredients like syrup or oil sufficiently destroys genetic material. It also will provide guidelines for which analytic methods processors should use to detect bioengineered material.