A recent report from the Congressional Research Service has a nice discussion of the ongoing developments associated with mandatory country of origin labeling for meat:
Less than one year after the COOL rules took effect, Canada and Mexico challenged them in the World Trade Organization (WTO), arguing that COOL has a trade-distorting impact by reducing the value and number of cattle and hogs shipped to the U.S. market, thus violating WTO trade commitments agreed to by the United States. In November 2011, the WTO dispute settlement (DS) panel found that (1) COOL treats imported livestock less favorably than like U.S. livestock (particularly in the labeling of beef and pork muscle cuts), and (2) COOL does not meet its objective to provide complete information to consumers on the origin of meat products.
This decade-long timeline of events was particularly helpful:
