The US Department of Labour filed a lawsuit against the owner of a beef-jerky maker after firing an employee who attempted to call 911 when a co-worker severed a thumb.

John M Bachman, president and CEO of Lone Star Western Beef Inc, is the focus of the federal lawsuit filed on Thursday. He could be forced to pay punitive damages and back pay to Michele Butler-Savage, the employee he fired.

The incident occurred in July 2014 at the company's former West Virginia plant when a worker, Chris Crane, severed part of his right thumb while operating a band saw. Ms Butler-Savage applied pressure to his wound and tried to call 911 with her mobile phone.

The lawsuit claims Mr Bachman ordered her to hang up her phone before 911 dispatchers could answer. She was sacked two days later.

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Mr Bachman apparently did not call for an ambulance, and instead instructed a supervisor to take Mr Crane to an urgent care clinic with his severed thumb. Mr Crane was ultimately transferred to a hospital where a reattachment procedure was unsuccessful, according to the lawsuit.

After the incident, Ms Butler-Savage told a US agriculture inspector that Mr Bachman failed to sanitise the area where her co-worker severed part of his thumb and reported that the plant lacked necessary protective equipment.

She filed a complaint with the Occupational Safety and Health Administration after losing her job. OSHA found that Mr Bachman violated federal whistleblower protections, and that Ms Butler-Savage’s attempt to call 911 was protected under federal safety and health laws.

“Lone Star Western Beef punished an employee for seeking emergency medical care for a seriously injured co-worker,” said OSHA regional administrator Richard Mendelson.

“No worker should have to fear retaliation from their employer for calling 911 in an emergency, or taking other action to report a workplace safety or health incident."