The National Distribution Union says employees at the Pacific Brands clothing factory in Palmerston North have been told the company has confirmed it will close the site.
Pacific Brands has previously said it is impossible to compete with cheap imports from China and other markets.
The union says the 50 employees have lived under the threat of closure for almost four months.
The company had been trying to sell the business, but the union says it has been told no formal purchase offer was made.
Union president Robert Reid says it is time for the Government to do more to stem redundancies.