Unite has pledged to work "strenuously" to see if the 350 jobs under threat at Welsh Country Foods can be saved.
Unite national officer, Julia Long described the announcement as "desperately sad news" and said the knock-on effect for the local economy could be "severe."
The news that Vion could shut its Welsh Country Foods site on Anglesey is a blow to those whowork there, the local community and the economy of the island.
This is a sad start to 2013 for our members and we will be doing all we can to ensure both support and a viable future for Welsh workers at Welsh Country Foods.
We need investment, not cuts to jobs in Wales and I will be raising this matter urgently with the Welsh Government
The leader of Anglesey Council will hold a meeting later today to discuss the possible closure of a meat processing plant on the island.
Around 350 jobs are at risk in Anglesey after Welsh Country Foods announced it has lost its key customer