(Bloomberg) -- BT Group Plc is dealing with a major coronavirus outbreak at a large call center, underscoring the risks of returning to workplaces while the pandemic surges in Europe.

BT confirmed that 36 of the 150 employees working at its office in Doncaster in northern England tested positive for Covid-19. All of the cases appear mild with no hospitalizations, and the people are now self-isolating, a spokeswoman for the London-based company said in response to questions from Bloomberg News.

The affected area and communal parts of the office have undergone repeated cleaning, and third-party contractors in the building have been informed, the spokeswoman said. The office was operating at less than 40% capacity to allow for social distancing, and about two-thirds of the staff have the option to work from home, she added.

“We’re in contact with Public Health England, and we’re following their advice and keeping them updated to reduce the risk of further contamination,” the spokeswoman said by email. “We continue to enforce strict hygiene and social-distancing measures in all of our contact centers, and to work hard to keep our people safe.”

Call centers have been repeatedly hit by Covid-19 outbreaks even as greater broadband use drives higher demand for telecom customer support. The U.K. government encouraged workers to return to workplaces in the summer, only to reverse its guidance in September and advocate six more months of home working as Covid-19 cases soared. Philip Jansen, BT’s chief executive officer, tested positive for Covid-19 in March.

A majority of call center workers across several industries said they thought they would catch the virus, in a Strathclyde University survey of 2,745 employees from unnamed businesses. Some said social distancing is impossible in their workplaces. Unions, including the Communication Workers of America, have called this year for employers to give their workers access to emergency paid leave and the option to do their jobs from home.

(Updates with context in fifth paragraph.)

©2020 Bloomberg L.P.