More than 100 jobs will be lost with the closure of Sealed Air's plant in Rotorua.
The plastic packaging manufacturer plans to shut down the site by the middle of next year and expand its Hamilton operation.
The Engineering, Printing and Manufacturing Union (EPMU) said the proposed closure would affect 112 staff, although many were expected to be offered re-employment in Hamilton.
EPMU manufacturing industry organiser Louisa Jones said the union had been working with Sealed Air, which had indicated it would offer generous relocation packages to ease the transition.
"For workers who do lose their jobs there'll be a union-negotiated redundancy package to help soften the blow," she said.
Ms Jones said the job losses were bad news for Rotorua, which has one of the highest unemployment rates in the country.
"There aren't a lot of other jobs in Rotorua at the moment, and the loss of these good, secure manufacturing jobs would be a real blow to the local economy.
"Increasingly the few jobs that are around are casual, part-time or poorly paid. The Government needs to act now to stop the decline in manufacturing and create good quality jobs in places like Rotorua."
The EPMU said the manufacturing sector in New Zealand had lost 17,000 jobs in the last year.