Four COVID-19 cases are now reported in staff at a prison in Kingston, Ont., where 80 inmates tested positive.
Correctional Service Canada says the employees work at Joyceville Institution, where a major outbreak was declared Thursday.
The outbreak has been linked to eight cases at two other prisons in Ontario.
The federal agency has suspended all in-person visits at its facilities in the province.
Prison authorities say all employees are actively screened for COVID-19 before entering the institutions.
They say all staff and inmates have been offered testing.