Union members at the Sistema Plastics factory in South Auckland have walked off the job for the fifth time.
The workers are demanding an end to employment contracts they say force them to work 60-hour weeks, on minimum wage with no overtime pay.
They also want changes made to contracts that consider workers to be part-time but still require them to work a 40-hour week.
The union, E tū, said they walked off the job at 9pm last night and are picketing outside the plant in Māngere this morning.
Sistema chief executive Drew Muirhead said he's disappointed by the strike action and is committed to continuing negotiations in good faith.