2 Sisters Food Group said it had found jobs for 290 of the 630 staff at the site in Smethwick, West Midlands, which will shut at the end of the month.
It said 250 workers had volunteered for redundancy and it was "working hard to explore all job opportunities" for the remaining 90.
Unite said some 300 workers faced redundancy and it believed this was "the only achievable outcome".
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The firm said the 290 it had found jobs for would be redeployed to its other sites in the West Midlands.
A spokesman said: "We are currently working hard to explore all job opportunities for the remainder of colleagues - 90 - over the next few weeks and are hopeful more roles will be found.
"It's with much regret that we have had to close one of the original 2 Sisters sites, but we have done our very best to find as many alternative roles as possible for colleagues."
Unite's national officer for the food industry, Julia Long, said: "Unfortunately, this still means that some 300 workers face redundancy.
"However, given the company's business case that this site was ageing and needed drastic modernisation to conform environmentally, we believe that this was the only achievable outcome."
A food processing factory is to close with the loss of hundreds of jobs.