About two-thirds of the Organic Valley headquarters in La Farge, Wis. was damaged by smoke and fire.
The LaCrosse Tribune reports that flames quickly spread through the walls of the building, located in Vernon County near LaCrosse.
Employees evacuated from the building watched as the executive offices and human resources department burned from the inside out. About 400 people work in the building.
No one was injured, and the cause of the fire is not clear.
Organic Valley is the nation’s largest co-operative of organic farmers.