Bakkavor in Newark, Nottinghamshire, saw the number of people who tested positive by rising from 20 to 39 on Friday.
The Nottinghamshire County Council said the peak is “a source of concern” and that now the 1,600 workers will be evaluated.
The company, which makes desserts for Waitrose and Tesco, said it had worked with fitness experts to implement strict protective measures.
Jonathan Gribbin, Director of Public Health at Nottinghamshire, said: “We know that Bakkavor has very intelligent controls, they have acted very responsiblely with us in public health, but we know that the greatest threat that citizens face is on the network and in the workplace.
“We focus on preventing [a local lockdown] and the only way to do that is for everyone to follow precautions and advice; social distance, dressed in masks and if you have to give in a car, you take precautions.”
Tests would be conducted at the plant for one week from Wednesday.
Shona Taylor, Bakukavor’s advertising director, said 50 other workers isolated themselves after contact with a positive colleague, and that cars leaving the site were checked to make sure they were covered in a mask if they shared cars.
The corporation has also translated posters and messages into languages.
“We have a lot of colleagues from Eastern Europe, many of them are Polish and we seek to use interpreters to make sure other people perceive what we’re trying to communicate,” Taylor added.
A check will also be set for members of the public starting Monday at the Newark and Sherwood District Council building.
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