Canada is requesting that the WTO form a compliance panel to review U.S. country of origin labeling rules, known as COOL, Canadian Agriculture Minister Gerry Ritz and International Trade Minister Ed Fast said on Monday. The move signals a new round in a dispute that could become a North American trade war.

Canadian cattle and hog producers say the rules, dating back to 2009, have led to lower U.S. imports of Canadian livestock because they created additional cost for U.S. packers.

Supporters say the labels offer consumers more information about where their food comes from.

Canada will not take retaliatory measures, which would involve tariffs on U.S. products including meat, cherries, rice and potatoes, until the WTO authorizes such action, the ministers said. Canada has previously said such a process could take 18 to 24 months.

The WTO ruled last year that the U.S. labeling rules were not in compliance with WTO obligations and ordered changes by May 23. The United States changed its labeling program, but Canada and Mexico have said the changes made the situation worse.

The U.S. Department of Agriculture declined to comment on Canada's move, but defended COOL.

"USDA remains confident that these changes will improve the overall operation of the program and also bring the mandatory COOL requirements into compliance with U.S. international trade obligations," said spokeswoman Michelle Saghafi.

The U.S. revisions include no longer allowing co-mingling of most muscle cuts from livestock in different countries within the same package. Meat and livestock groups from the United States and Canada launched a U.S. court action last month aimed at striking down the stricter rules.

(Reporting by David Ljunggren in Ottawa and Rod Nickel in Winnipeg, Manitoba; editing by Maureen Bavdek and Matthew Lewis)