Barnsley Council confirmed last week that there has been a total of six positive cases the Barnsley town centre hub.
The building, on Pitt Street, underwent a deep clean last Monday following reports of positive cases, before the venue was closed last Wednesday.
Julia Burrows, director of public health at Barnsley, said: “We’re aware of a six positive confirmed cases of coronavirus at Barnsley’s Royal Mail sorting office, with further cases possible as investigations and staff testing continues.
“A number of staff are self-isolating.
“Barnsley Council’s regulatory service team and colleagues from Public Health England are working with Royal Mail to understand how the virus is being spread across the workforce; looking at possibilities inside and outside of the premises and what we can do to reduce and prevent this.
“A number of measures have been implemented to prevent the spread of coronavirus on the site, and these will be reviewed with the company.
“The council is working closely with Royal Mail to provide advice and support and are in the process of reviewing risk assessments.
“Regulatory services officers will be inspecting the premises following the deep clean, once it is back up and running.”