– Last Friday, Vermont implemented the country’s first law that makes food distributors reveal the presence of genetically engineered ingredients.

In a few weeks, that law could be dead.

The battle over mandatory on-package disclosure of genetically modified organisms — GMOs — is coming to a boil once again in the U.S. Senate. In March, Congress’s upper chamber could not find the support to bring a national labeling bill to a vote because the legislation would have outlawed state GMO statutes while also banning any national mandatory on-package GMO labeling.

This week, the Senate will likely debate a bill that outlaws state GMO labeling statutes but replaces them with a national mandatory standard.

The bill, negotiated by the Republican chairman of the Senate Agriculture Committee and the ranking Democrat, would kill the Vermont law, while delaying implementation of new federal GMO labeling rules for two years. The federal bill does not designate fines for violations. It offers several options for on-package designation of GMOs, including words, a symbol developed by the U.S. Department of Agriculture or a smartphone scan code. Any of those markings on packages would signal the presence of genetically engineered ingredients.

Industry and some consumer groups have indicated support for the bill, while some labeling advocates oppose it, saying it is weaker and less transparent than the Vermont law.

Minnesota’s biggest food companies have expressed support for the Senate bill, citing the need for a national standard that avoids a patchwork of state laws. But General Mills and Hormel also have adjusted product packages to comply with the Vermont law and will distribute those packages nationwide. Land O’Lakes and Schwan Food Co. did not respond to questions last week about whether they will sell in Vermont with new packaging.

The Des Moines Register reported last week on a letter by the U.S. Food and Drug Administration that questioned the new federal bill’s definition of “contains genetic material.” The letter said the phrase could be interpreted to exclude products made with genetically modified ingredients that disappear in the course of processing.

Sign-carrying protesters decrying what they consider the federal ­proposal’s loopholes gathered outside Sen. Amy Klobuchar’s Minneapolis office last week. They urged Klobuchar, a member of the Agriculture Committee, to reject the new bill in its current form. A demonstration is planned at Sen. Al Franken’s office next week, when the bill is supposed to be considered on the Senate floor.

Klobuchar and Franken said they are studying the bill to decide whether to vote for it. Both voted against the earlier proposal in March.

The new bill “has huge loopholes for foods that would be exempted,” said Heather Kurth Flesland of Right to Know Minnesota, one of the protest’s organizers. “Soy and canola oil could be exempted, as well as sugar from genetically modified sugar beets. It takes the Vermont law down and waits two years to put in new labels. It is an absolute gift to the food industry.”

Other supporters of mandatory GMO labeling like Just Label It and the Organic Trade Association have offered a measured blessing.

“We support national mandatory GMO labeling, but we believe the Senate needs to clarify,” explained Scott Faber of the Environmental Working Group and Just label It. “This is not a GMO bill if it excludes GMO oils and sugars. Any food that contains ingredients derived from genetic engineering should be labeled.”

If the new bill passes the Senate, it must still pass the House, which earlier voted for a bill that places a national ban on on-package GMO disclosure.

Until all of that happens, Vermont’s law stays in place. As the federal process plays out, the state plans a phase-in process which will allow older, unlabeled inventory to stay on shelves until year’s end, said Kyle Landis-Marinello, an assistant attorney general in the state’s environmental protection division. Even then, enforcement will be largely complaint-driven with a focus on companies that knowingly break the law.

The Vermont Retail and Grocers Association has not confirmed the names of any major manufacturers who have withdrawn from the state over the labeling requirements, said Erin Sigrist, the group’s president-elect. The grocers association has heard rumors that some companies, including “national brands you would definitely know,” will not comply with the new law, but the association has not reached them for explanations, she explained.

Coca-Cola got virtually all of its products repackaged but is still working on 16-ounce individual cans of soda, Sigrist said. Mead Johnson, a maker of baby formula, will not be shipping until it finishes packaging changes, she added.

“It’s kind of a waiting game to see how things go,” Sigrist said.