Authorities in the Netherlands recalled 50,000 tons of meat marketed as beef that may contain horsemeat.

Two Dutch companies, Wiljo Import en Export B.V. and Vleesgroothandel Willy Selten B.V., supplied the meat to more than 500 companies across Europe, but they cannot trace the exact source of the meat. 

Esther Filon, spokeswoman from the Netherland’s Food and Consumer Product Safety Authority told the Associated Press, “If meat has an unclear source then the law—the general food law—says it is no longer fit for human or animal food.”

The recall covers meat from Jan. 1, 2011, through Feb. 15 of this year when the companies came under investigation for the tainted meat. In total, 132 companies in the Netherlands and 370 companies around Europe are affected by the recall. 

Part of the fear stems from the possibility that the meat was tainted with phenylbutazone, which is a banned substance for human consumption.

Asda, a British branch of Walmart, recalled their Smart Price Corned Beef on April 9 after tests showed “very low levels of horse medication called phenylbutazone.” The product was first taken from shelves in March when it tested positive for more than 1 percent horsemeat.