A recent World Trade Organization (WTO) ruling that the U.S. "dolphin-safe" label discriminates against Mexican tuna fleets is causing concern among some U.S. environmentalists.

Their major fear: The United States would have to sacrifice an important environmental law in the name of free international trade.

At issue are Mexican fleets that rely on chasing-and-netting techniques that can harm and kill dolphins.

It's not clear what the ruling, issued May 16, will mean for the future of the voluntary dolphin-safe label, but environmentalists are worried.

"This latest ruling makes truth-in-labeling the latest casualty of so-called 'trade' pacts, which are more about pushing deregulation than actual trade," Todd Tucker, research director for Public Citizen's Global Trade Watch, said in a news release.

"Members of Congress and the public will be very concerned that even voluntary standards can be deemed trade barriers."

The Mexican government had challenged the United States' dolphin-safe label with the WTO, saying it discriminates against Mexican tuna fleets. Last fall, a dispute panel ruled in favor of Mexico on some issues but acknowledged the United States had a legitimate consumer and environmental right to pursue the label. Mexico and the Office of the U.S. Trade Representative, which handles dispute cases before the WTO, appealed the case.

In the final ruling, the WTO appeals court sided with one of Mexico's major concerns: "The appellate body reasoned that, by excluding most Mexican tuna products from access to the 'dolphin-safe' label while granting access to most U.S. tuna products and tuna products from other countries, the measure modifies the conditions of competition in the U.S. market to the detriment of Mexican tuna products."

Nkenge Harmon, deputy assistant for public and media affairs for the U.S. trade representative, said via email the United States "will study the report carefully and consider its implications."

Harmon said the government viewed the appellate court's ruling as a mixed bag, confirming the label provides important consumer and environmental protections but deciding it did not offer equal protections to dolphins across the world's oceans. Mark Palmer, associate director of the International Marine Mammal Project for Earth Island Institute, noted the U.S. government has 15 to 19 months to "negotiate a way for the United States to come into compliance" with the WTO ruling. He said Earth Island will push the Obama administration to try to persuade the Mexican government and its fishing fleets to adopt more dolphin-safe methods.

Palmer noted Mexico can sell tuna in the United States, just not under the U.S. Department of Commerce's dolphin-safe label.

Regardless of the May 16 ruling, the three major U.S. tuna processors — Bumble Bee, StarKist and Chicken of the Sea, which collectively sell more than 80 percent of the canned and pouched tuna in the U.S. — claim they will not alter their tuna-buying practices.

"For those companies, their commitment to dolphin-safe tuna is unwavering," says Gavin Gibbons, spokesman for the National Fisheries Institute's Tuna Council, which represents the three processors.