The United States lodged an appeal on Friday to challenge a World Trade Organization ruling that said it had failed to bring its meat labeling laws into line with global trade rules.
Canada and Mexico won a WTO ruling three years ago that said the U.S. rules illegally discriminated against imported meat.
The United States lost a subsequent appeal and was told to bring its laws into line, but in October this year the WTO said it had not done so, paving the way for Canada and Mexico to demand the right to impose trade sanctions.
Even if the latest U.S. appeal fails to overturn October's ruling, it will delay the threat of sanctions, which would only be imposed if the United States failed to bring its laws into line with the WTO rules within a reasonable period.
After that, Mexico and Canada could ask the trade body to let them impose a certain degree of trade sanctions on the United States, which in turn can challenge such a ruling.
Canada estimates U.S. rules requiring retailers to list the country of origin on meat cost its farmers and processors $1 billion a year in lost sales and lower prices, and Mexico has said it would seek "hundreds of millions" of dollars if the U.S. does not change its rules.
The U.S. rules have resulted in fewer Canadian pig and cattle exports since 2009, according to the Canadian government. Canada already has published a hit-list of potential U.S. targets including wine, chocolate, ketchup and cereal.
