New European Union rules from April, 2010, include measures to ensure agents commonly used in horses, such as phenylbutazone, cannot enter the human food chain.
"We have known of the dangers of chemicals in American horsemeat for years, but our warnings have often fallen on deaf ears," said Jerry Finch, founder of Habitat for Horses, the nation's largest all-breed equine rescue organisation.
"Thankfully, agencies in the European Union responsible for health safety realised that there is virtually no testing for dangerous chemicals in American horses being sold for food.
"Foreign governments will inadvertently bring the slaughter of American horses to a halt while the American government, with their failure to pass legislation, has simply ignored the health of the European people."
Finch says that the same EU rules will halt the export of American horses slaughtered in Mexico for European consumption.