The Kansas City, Mo.-based cooperative's supply agreements in eastern Louisiana and Florida are reportedly being examined as part of the probe. Earlier this month, DOJ investigators and representatives from the Louisiana and Florida attorney general offices met with Louisiana producers. DFA says the DOJ has not yet contacted the co-op regarding this investigation, and that over the years each of its numerous acquisitions, mergers and business ventures have passed DOJ scrutiny.

Last year the DOJ sued DFA in a similar case in Kentucky. Two years ago it was DFA's involvement in a proposed merger of HP Hood and National Dairy Holdings that soured the deal.

DFA claims to be the largest cooperative in the United States, and is said to control as much as a third of the nation's milk production.