A spokesperson for CNH Industrial America, which manufactures agricultural and construction equipment, said two contractors were involved in the incident at the Case Tractor Factory, which the company owns.
The spokesperson said the company is cooperating with the investigation.
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"Our thoughts are with them (the workers) and their families during this difficult time," the spokesperson said. "At this time, we are focused on providing support to those affected and ensuring the safety of all our employees and partners."
It was not immediately clear what caused the workers' injuries.
Occupational Safety and Health Administration officers responded to the incident, a regional spokesman for the U.S. Department of Labor said.