President Obama signed a bill Friday that requires all food companies to label products with genetically modified ingredients for the first time.

Congress two weeks ago passed the legislation mandating most foods carry an on-package label with words, a symbol or a smartphone scan code disclosing the presence of GMOs.

The U.S. Department of Agriculture has two years to write the rules, pre-empting a GMO Vermont law that kicked in earlier this month.

Food companies initially fought for voluntary labeling but eventually acquiesced to the compromise. Food makers argue GMOs are safe, but skeptics had pushed for stricter laws over fear of possible health and environmental risks.

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.

Two Minnesota companies, General Mills and Hormel, had already rolled out on-package GMO labels on their products in anticipation of Vermont’s laws. Other Minnesota firms, Land O’Lakes and Cargill, eventually supported the legislation as well.

“This is an extremely positive development for consumers who want more information about the food they purchase and consume and for the food industry who now has a national, uniformed labeling standard,” Cargill said in a statement Friday.

Lobbying efforts will now pivot toward the USDA as it defines the rules for implementing the law.

A likely point of contention will be making a distinction between foods with GMOs and those made with GMOs during processing but that contain nearly no trace of them in the final product.

Some GMO critics are worried the smartphone code doesn’t offer enough transparency.

But the bill requires the USDA to study any potential problems consumers face with the scan code within a year after use begins.

 

The Associated Press contributed to this report.