U.S. meat producer Glenn Valley Foods was operating an Omaha, Nebraska, facility with about 30% of its staff on Wednesday after federal agents detained workers in an immigration raid the previous day,

Immigration authorities raided an Omaha meat production plant Tuesday and took dozens of workers away in buses, leaving company officials bewildered because they said they had followed the law.

“U.S. Immigration and Customs Enforcement, and federal law enforcement partners, executed a federal search warrant at Glenn Valley Foods, today, based on an ongoing criminal investigation into the large-scale employment of aliens without authorization to work in the United States,” said a statement from Tanya Roman, ICE spokesperson.