Omaha, Nebraska - A food sanitation company is under investigation for allegedly hiring children to work graveyard shifts at various locations in the US.

On Thursday, the US Department of Labor (DOL) filed a temporary restraining order against Packers Sanitation Services (PSS), a company that cleans meat packing plants and slaughterhouses across several Midwestern states.

In a statement, the DOL said their investigation found that the company "employed at least 31 children – from 13 to 17 years of age – in hazardous occupations" and several minors "suffered caustic chemical burns and other injuries."

"Some children reported working long hours or overnight shifts. Other children reported working on power-driven machines or on the kill floor," the order stated.

A spokesperson for PSS told NBC News that it "has an absolute company-wide prohibition against the employment of anyone under the age of 18 and zero tolerance for any violation of that policy - period."

Federal law bars children under 14 from working in any capacity, and only allows those in school to work no more than three hours a day. Those who are not in school may work no more than eight hours per day.

The Department of Labor also accused the company of attempting to interfere with their investigations, resulting in District Judge John Gerrard issuing an injunction that orders the company to comply.