The U.S. Department of Agriculture said Thursday that Boar's Head processing plants nationwide are being investigated by law enforcement following a deadly listeria outbreak linked to the company's deli meats.

At least 59 people have been hospitalized and 10 have died due to the outbreak traced to products from a now-closed Virginia plant. The facility had a history of violations, including mold and insect problems, according to records obtained by CBS News.

The probe came to light Thursday when the company denied a CBS News request for info on the company's Michigan, Arkansas, and Indiana plants. The USDA's Food Safety and Inspection Service confirmed an investigation was underway, but did not reveal details, saying that releasing records "could hinder the government's ability to further control and shape the investigation."

It's unclear if the investigation is criminal or civil.

Meanwhile, Connecticut Democrats Sen. Richard Blumenthal and Rep. Rosa DeLauro on Thursday called on the USDA and the Department of Justice to consider criminal charges against Boar's Head.

In a letter to the agencies, they wrote, "The time for action is long overdue, and we urge your agencies to work together to seek immediate justice for impacted consumers and to prevent this from happening again."

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