Poultry producer 2 Sisters in Anglesey has suspended production and closed its factory after the number of workers testing positive for coronavirus rose to 158.
According to the BBC all staff at the 2 Sisters meat processing plant in Llangefni are now self-isolating, with further workers confirmed with the virus last Thursday.
Public Health Wales (PHW) said the number of cases was expected to rise.
Economy minister Ken Skates said it was essential to make sure the Anglesey outbreak was "kept as local as possible".
Anglesey council has already confirmed schools will not reopen as planned on 29 June following incidents at the plant.
The BBC story confirmed that 2 Sisters had said "the health, safety and well-being of our colleagues is ultimately the thing that matters most at our business. We will not tolerate any unnecessary risks – however small – for our existing loyal workforce at the facility."