Sealed Air elected union delegate Gillian Tangi said it was a sad day for workers.
"We knew it was coming, but not this quickly. Everyone was given the day off so they could tell their families."
Ms Tangi said she understood the majority of workers would be made redundant with about 30 positions available at the company's Hamilton site.
"Many of the younger workers have already said Australia is looking like more of a reality for them, there are not many jobs for them here.
"But for the older workers, they are not sure what's going to happen ... there's a long, sad 10 months ahead of us," she said.
Engineering, Printing and Manufacturing Union manufacturing industry organiser Louisa Jones said the union was working with Sealed Air to soften the impact of the closure but the proposal was bad news for Rotorua.
"For workers who do lose their jobs there'll be a union-negotiated redundancy package to help soften the blow.
"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."
The Sealed Air site has been earmarked for a convenience retail complex, to be known as Lynmore Junction, by the site's owners the Holmes Group. The development would include a supermarket and is expected to create up to 300 jobs. A resource consent hearing is set down for June 11 and 12. Sealed Air holds a lease on the site which expires in September 2014.
Rotorua Labour Party spokesman Fraser Newman said it was a blow for Rotorua.
"While I'm confident that some sort of arrangement will be worked out with the employees, the government needs to create an enabling environment for companies to grow and take on more staff. Otherwise, we have people simply unable to find meaningful work."
Rotorua MP Todd McClay said whilst the loss of any job was of concern the proposal to redevelop the site would mean a gain of about 200 jobs.
He said it was important Sealed Air met its obligations to workers and he would be talking to the Ministry of Social Development to see what help was available to get them into on-going employment.
Mr McClay said he believed there was good reason to be optimistic with regard to job creation in Rotorua.
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