More than a dozen companies have recalled millions of pounds of potentially contaminated food in recent days in a new challenge for food producers facing heightened scrutiny of the U.S. food supply.

Food manufacturers across the country are recalling nearly 4 million pounds of food shipped to grocery stores and distributors nationwide, after a Canadian supplier recalled vegetables used as ingredients in their food. The U.S. Department of Agriculture and Food and Drug Administration said they are investigating because the vegetables...