Nicola Sturgeon has described a coronavirus cluster linked to a food processing plant in Coupar Angus as "complex and potentially significant."
Ten cases - at least seven employees and two people in the community - have been linked to the 2 Sisters plant, which closed yesterday.
The first minister said she would be "very surprised, albeit pleasantly" if that number did not rise.
The entire workforce will now be tested at a mobile testing unit at the site.
All workers will also have to self-isolate for 14 days.
Speaking during her daily coronavirus briefing, Ms Sturgeon said that contact tracing in connection with the cluster was ongoing.
"This is a complex and potentially significant cluster," she said.
"In addition to the overriding public health concern relating to the outbreak, the closure of the plant potentially, of course, has an economic impact, and we also need to consider possible animal welfare issues."
Ms Sturgeon said animals that would have been sent to the plant in the next few days would not now do so.
She added: "So for all of these reasons, we are monitoring all aspects of this situation very carefully and closely, and we will provide further information in due course as and when it becomes available."
NHS Tayside Public Health was first alerted to the outbreak on Sunday..