When the Food and Drug Administration approved the commercial sale of genetically engineered AquaAdvantage salmon in November, the agency made an important stipulation: The fish could only be produced in Canada and Panama. Additionally, no label declaring that the salmon had been genetically modified would be required.

Now, critics of the fish, which would be the first-ever genetically engineered animal protein sold in the U.S., are leveraging the limited geography of production the FDA allowed to challenge the lack of labeling regulations—and pushing the day when GMO salmon steaks show up at the seafood counter further down the road. On Friday, the FDA issued an import ban on GMO salmon until labeling standards can be established, following a directive passed by Congress late last year. The ban effectively makes it impossible to stock and sell the salmon in the U.S. in the near term.

When the FDA approval was announced last year, AquaBounty Technologies, the Massachusetts-based company that developed the fast-growing salmon, told TakePart that “it is too early to discuss commercialization plans, but there are several paths to market that are being considered,” including selling the fish under a brand name.

Still, without a labeling requirement from the FDA, there was concern among pro–GMO labeling groups that genetically engineered salmon could simply be sold as farmed Atlantic salmon. A 2014 Consumer Reports survey found that 92 percent of Americans believe GMO salmon should be labeled. But another 2014 survey—conducted by the International Food Information Council, a consumer education nonprofit that receives industry funding—found that 59 percent of Americans were “somewhat” or “very” likely to buy GMO salmon.

“This is a huge step in our fight against ‘Frankenfish,’ ” Sen. Lisa Murkowski, R-Alaska, who added the import ban to the omnibus spending bill Congress passed in December, said in a statement. The wild Alaskan salmon catch was valued at $414 million in 2015. “I firmly believe that mandatory labeling guidelines must be put in place as soon as possible so consumers know what it is they are purchasing. It seems that the FDA has begun to listen, and I hope this is a sign that the agency plans to develop these necessary guidelines,” she said.

The ban, according to a statement from AquaBounty CEO Ronald Stotish, “has no impact on AquaBounty’s operations, as we are not currently importing our salmon into the United States.” But if the company does start to import its product and retail sales begin, the fish will almost certainly bear some sort of label saying that it has been genetically modified.

Ahead of the FDA approval of AquaBounty salmon—which uses an added gene to make the fish grow up to twice as fast—Target, Whole Foods, Kroger, Trader Joe’s, Costco, and Safeway have all said they will not sell GMO salmon.