Foodmakers will soon be required to disclose when their products contain genetically modified ingredients —but those labels may not be as obvious, or as comprehensive, as consumers expected.

Food products may be exempted from labeling if they are made with some refined GM sugars and oils, or if a product contains GM ingredients in amounts that fall beneath a predetermined threshold, according to a proposed rule released by the Agriculture Department on Thursday.

The proposed rule also instructs foodmakers to use the term “bioengineered” to label GM foods instead of “genetically modified,” a more recognizable phrase.

The proposed rule, which will now undergo a public comment period and could be finalized as early as this summer, represents a major milestone in the complicated, yearslong process to regulate the labeling of GM foods. Congress passed a mandatory-labeling law in 2016, but implementation has been delayed by questions about which foods should be covered and what types of labels foodmakers should use.

Food and consumer groups said they were happy to see the rules move forward, though some expressed concern about provisions they say could leave many products excluded and many shoppers confused.

“We think, at the most fundamental level, consumers expect the mandatory GM labeling standard to apply to all GM foods,” said Colin O’Neil, the legislative director for the Environmental Working Group.

The proposed rule provides the best glimpse so far into what mandatory GM labels will look like — while still leaving some questions open.

Food companies will have three options for disclosing GM ingredients, the USDA said: a one-sentence label declaration, such as “contains a bioengineered food ingredient”; a standardized icon, like that used in the National Organic Program; or a QR code or other digital marker that directs shoppers to a website for more information. In a statement, the Grocery Manufacturers Association praised the flexible standard, pointing out that it has already put QR codes on 25,000 products through its SmartLabel program.

“We welcome the release of the proposed rule ... and will be working with our member companies to review and develop comments on the draft rule and the USDA questions,” the association said in a statement. “Our comments to USDA will reflect the ongoing commitment of our member companies to providing consumers with the transparency they need to make informed product choices.”

As to which foods will be considered genetically modified, the USDA has proposed a number of options. Under one plan, the USDA said it would exempt highly refined sugars and oils, such as those made from GM corn, soybeans and sugar beets, from labeling, on the grounds that the refinement process screens out modified DNA. Consumer groups have warned that this would effectively exempt as much as 70 percent of covered food products from GM labeling.

Under another plan, the USDA would exempt products containing ingredients from mixed GM and conventional sources that were less than 5 percent GM by weight. While that represents a tiny amount overall, it is significantly higher than the 0.9 percent threshold observed by China, Russia and the European Union, as well as by the Non-GMO Project, a voluntary initiative.