The Dutch food group Vion which employs hundreds of meat and poultry processing workers in Wales says it is selling all its operations in Britain.
The company runs abattoirs and processing plants on Anglesey, Sandycroft in Flintshire and other sites in Wrexham and Merthyr Tydfil.
It employs 13,000 at 38 UK sites. Vion said it is confident it will sell its UK sites as viable businesses.
As well as workers, unions said the plans could hit farmers.