The Meat Workers Union says it had no warning that the future of the Alliance Group plant at Sockburn in Christchurch was under review.
Alliance is starting a consultation process with 250 employees and unions on a proposal to close the plant at the end of the 2012 processing season between May and July next year.
Alliance processes cattle, deer and pigs at Sockburn and also does some lamb cutting.
The company says the plant has not run at a profit in recent years and it is proposing to transfer operations to other sites.
The union says it is unusual to get such advanced warning about meat plant closures.
"It's the first time we've had a decision from the company like that gives a full season warning that the plant's going to close,'' said national secretary Dave Eastlake.
"I suppose it has its advantages for some of the people there - it gives them time for them to think about their future ... and that may be the reason Alliance made such an early decision to make it public.
"In spite of that, it takes a good hunk of jobs out of the Christchurch area and that's sad for an area that's had enough problems in the last 12 months."
Alliance says if it goes ahead with the closure, it will offer Sockburn employees the chance to transfer to jobs at other plants.
Chief executive Grant Cuff says beef and venison processing would be transferred to other plants in South Canterbury, North Otago and Southland.