"Any injury like this is life-changing and horrific, you cringe just thinking about it."
Watt said the union was yet to speak to the man, but were trying to contact him.
"We've got between 400 and 500 members working [at Alliance Smithfield]."
Watt said senior management at Alliance Smithfield had called him yesterday, and said they would be launching an independent investigation.
A St John spokesman said the man, in his 40s, was taken to Timaru Hospital.
A WorkSafe spokeswoman said they are investigating so were unable to provide any further information.
Alliance Group procession general manager Kerry Stevens confirmed an employee was injured at the plant on March 17.
"We've launched our own inquiry and we're co-operating fully with WorkSafe and their investigation. We're supporting the employee, his family and colleagues."