More than five tons of genetically engineered Atlantic salmon are on their way to U.S. restaurants and food service outlets where customers will not be told what they’re eating.

Federal labeling law “directs” companies to disclose genetically modified ingredients through use of a QR code, on-package wording or a symbol. Mandatory compliance takes effect in January 2022, but the rules don’t apply to restaurants or providers of meals away from home.

The Associated Press reports thus far, the only customer to announce it is selling the salmon is Samuels and Son Seafood, a Philadelphia...