Russia will ban U.S. turkey products over concerns about the controversial animal drug ractopamine, the country’s Veterinary and Phyto-Sanitary Surveillance Service (VPSS) announced this week. The news comes a few days after Russia announced it will block U.S. beef and pork as of Feb. 11 due to a lack of compliance to its zero-tolerance policy for ractopamine residues in meat and poultry products.

A USDA spokesperson said the department is “extremely concerned” with Russia’s recent actions, which jeopardize more than $500 million in U.S. meat exports.

The U.S. Food and Drug Administration approved ractopamine as safe— for boosting growth and leanness in pigs in the weeks leading up to slaughter—in 1999 and has since approved the drug for use in cattle and turkeys. More than two dozen other countries, including Canada and Brazil have given the feed additive the green light, but the substance remains prohibited in China, the European Union, and many other countries.

Last summer, the Codex Alimentarius Commission ended a years-long dispute over whether to approve an international standard for maximum residue limits for ractopamine in beef and pork products. The commission approved the standards in an unusually contentious vote, 69-67, but trade disputes over the drug have continued.

The USDA is urging Russia to adopt the Codex standards, which allow for residues at or below 10 parts per billion in muscle meat. The department says it has not received any scientific evidence from Russia that would justify the country’s ban and U.S. officials have offered to host technical consultations on the issue, to no avail.

“We continue to call on Russia to suspend these unjustified measures and restore market access for U.S. beef, pork and turkey,” said a spokesperson. The USDA did not respond to questions about what portion of the beef, pork, and turkey markets utilize the drug.

Russian media outlets reported Thursday that the country’s health officials were not accepting assurances from the United States that ractopamine is safe in meat at very low levels.

“We, as a WTO member, have not received sufficient proof. The proof that has been presented does not satisfy us. It does not stand up to criticism in terms of the methodology and the time over which the drug’s application was analyzed, and it does not answer the question regarding the drug’s accumulation in a human body,” said Gennady Onishchenko, Russia’s chief public health officials who heads the government’s consumer watchdog, in an interview with Interfax Thursday.

Onishchenko also pointed out that two U.S. advocacy groups, the Center for Food Safety and the Animal Legal Defense Fund, recently petitioned the FDA to re-evaluate the drug’s implications for human health and animal welfare.

Outside of Russia, China and the EU, which together produce and consume the vast majority of the world’s pork, have been the most outspoken opponents of ractopamine use in meat production.

China has expressed concerns about the higher concentrations of ractopamine residues found in pig organs, which can be part of a traditional Chinese diet, and the EU has argued that the science backing the drug’s safety is flawed.

In 2009, the European Food Safety Authority published a 52-page report strongly criticizing the data and methodology used by Codex to calculate the Acceptable Daily Intake for ractopamine, upon which the ractopamine residue standards are based.

A report last year by the Food and Environment and Reporting Network found that, according to FDA data, more pigs were reported to have experienced adverse effects from ractopamine than any other veterinary drug.

“Pigs suffered from hyperactivity, trembling, broken limbs, inability to walk and death, according to FDA reports released under a Freedom of Information Act request. The FDA, however, says such data do not establish that the drug caused these effects,” read the report.

A handful of studies have linked ractopamine, which is sold commercially as Paylean, to increased aggression and hyperactivity in pigs.