Nearly 100 workers at two food processing plants which supply to Tesco and other supermarkets have tested positive for coronavirus.
Public Health Wales confirmed 58 cases at 2 Sisters chicken factory in Llangefni on Anglesey, with more than 200 people said to be self-isolating.
In Wrexham, 38 staff have tested positive at Rowan Foods, which makes food for supermarkets across the UK.
Health Minister Vaughan Gething said the outbreak was a "concern".
He said it "reiterates the importance of social distancing and hand hygiene".
Other countries have also recorded outbreaks in meat processing plants, including in
iFrance and the US, where workers in at least two food factories have died amid outbreaks.
2 Sisters, which has contracts with KFC, Tesco and Marks & Spencer has suspended production and closed following the outbreak.
As of Wednesday, union officials said they were aware more than a third of the 560-strong workforce at the Anglesey chicken processing plant were self-isolating.
The company had introduced thermal temperature checks and employed marshalls to ensure social distancing was maintained.
Meanwhile Rowan Foods, which employs 1,500 people, said 38 staff were "absent due to testing positive for Covid-19".
The company, owned by Oscar Meyer Quality Foods, makes prepared foods for companies across the UK, including Aldi, Asda, Sainsbury's and Tesco.
In a statement, it said none of the staff were "seriously ill or had been hospitalised" and contact tracing was taking place.