Public Health Wales (PHW) says it has identified 51 cases of Covid-19 associated with the 2 Sisters abattoir on Anglesey.
North Wales Live revealed last week that three workers had tested positive for Covid-19 at the Llangefni chicken processing site.
The outbreak spread among the workforce with 13 positive cases confirmed on Monday and this morning it was confirmed the site would close for two weeks.
Workers said they were "scared" as the outbreak spread through the site.
Now health chiefs have confirmed there are 51 cases related to the site.
“Our priority is to bring this outbreak to a swift conclusion,” said Dr Christopher Johnson, consultant in health protection for Public Health Wales.
Unite the union is now in discussions with 2 Sisters to secure full pay for those workers during the shutdown.
The company, which employs 560 people at Llangefni, supplies supermarket brands like Tesco as well as fast food chain KFC.
A 2 Sisters spokesman said: "The health, safety and wellbeing of our colleagues is ultimately the thing that matters most at our business. We are a responsible company with people at its core. Without our people we are nothing.
"Therefore in light of the current Covid-19 cases at our Llangefni site, we have decided to take the necessary action to clearly demonstrate how seriously we take this issue by doing the right thing.
"Doing the right thing means from today (Thursday June 18) we will temporarily suspend production at our Llangefni site with immediate effect for a period of 14 days.
"We will not tolerate any unnecessary risks – however small – for our existing loyal workforce at the facility.
"We have worked in close collaboration in the past week with Public Health Wales, Anglesey Council, the Health & Safety Executive, the FSA and the Unite union who have all offered great advice, scientific knowledge and support, and we thank them for their help and guidance, which has informed this decision.
"Our sole focus now is to ensure we support all our colleagues through this time and look forward to operating safely and securely in 14 days time."
