Some 42 members of staff at a seafood plant in Co Down have tested positive for Covid-19.
Kilkeel Seafoods has closed its premises where 250 staff are based for a deep clean.
Mobile testing units moved into Kilkeel last month following the identification of the Delta variant of the virus in the area, which has since become the dominant strain in Northern Ireland.
A spokesperson for Kilkeel Seafoods said staff testing had been requested as a preventative safety measure after a small number of positive cases were reported among workers last week.
They said the company had been working under strict Covid-19 guidelines, employing stringent use of social distancing and protective equipment.
South Down MP Chris Hazzard has expressed concern at the development.
“It’s hugely concerning that over 40 staff have tested positive for Covid-19 at Kilkeel Seafoods,” the Sinn Fein man said..
“My thoughts are with all the staff impacted by this outbreak and their families.”