Federal immigration agents on Monday arrested at least 300 people during a raid at a Postville meat processing plant.

The raid by agents from U.S. Immigration and Customs Enforcement was the largest such operation in Iowa history, said Matt M. Dummermuth, U.S. Attorney for the Northern District of Iowa.

Dummermuth said the raid at the Agriprocessors Inc. plant came after months of planning. Agriprocessors is the world's largest kosher meatpacking plant.