Mexico has suspended purchases of meat from 30 U.S. plants and the question is why. The plants are located in 14 states. Shipments were turned back at the border last Wednesday, surprising producers and the U.S. government. The initial speculation was that Mexico was retaliating for COOL, the regulation that requires meat (and other products) to have their country of origin on the sales label. Canada has filed a complaint with the World Trade Organization saying the Country of Origin Labeling (COOL) regulation violates trade treaties. Mexico joined that complaint the week before turning away the meat shipments. The U.S. Department of Agriculture says the shipments were turned back because of Mexican concerns about sanitation at the plants.   Mexican officials denied that COOL was behind the dispute. Reports this morning said the banned U.S. meat production plants could be reinstated today. Mexico buys 27% of the beef exported from the U.S.