WASHINGTON (AP) — President Barack Obama has signed into law a bill that will require labeling of genetically modified ingredients for the first time.

The legislation passed by Congress two weeks ago would require most food packages to carry a text label, a symbol or an electronic code readable by smartphone that indicates whether the food contains genetically modified organisms, or GMOs.

The Agriculture Department has two years to write the rules, which will pre-empt a Vermont law that kicked in earlier this month.

The food industry says 75 percent to 80 percent of foods contain genetically modified ingredients — most of those corn and soy-based. The Food and Drug Administration says they are safe to eat.