An eight-day strike at the Open Country Cheese factory at Waharoa near Matamata will go ahead from 6pm on Wednesday, a union says.
The Dairy Workers Union gave notice of strike action a fortnight ago following what it says was a refusal by the management of Open Country Dairy to negotiate a collective agreement.
Last week, compulsory mediation talks between the company and the union failed to resolve the dispute.
National Secretary James Ritchie says the employer has chosen to lock out workers from 24 September for six weeks or until such time as the workers choose to return on the company's terms and conditions of employment.
Mr Ritchie says the company is refusing to recognise the right of workers to join a union and bargain collectively.
The union says 38 workers or a little over half of the workforce, are taking strike action.
The plant, which operates 24 hours seven days a week, has the capacity to process two million litres of milk a day.
Open Country Dairy chairman Laurie Margrain says the company will keep the plant running by staffing it with managers, directors, employees from elsewhere in the company, shareholders and farmers.
He says none of the company's workers at its whole milk powder plants in Wanganui or Awarau in Southland are part of a collective contract.
The company also has plants at Wanganui and in Southland processes about 800 million litres of milk a year.