Police have launched an inquiry after a Student Loans Company office had to be evacuated when a member of staff opened an envelope and white powder came out.
Emergency services were called to the firm's offices in Darlington, County Durham, when an employee reported feeling unwell.
The staff member was treated at the scene and recovered, and the building later was given the all-clear for the next shift.
The suspect powder was found in an A4 envelope at the company's offices in McMullen Road.
Derek Ross, director of operations at Student Finance England: "We took the decision to send staff home from Student Finance England in Darlington earlier today, as police carried out their investigations.
"The Darlington site is now safe and staff will return for their next shift as normal.
"We have taken steps to ensure there is minimum disruption to our customer service.
"Our Student Finance England calls are being answered at our other sites.
"Our dedicated EU student phone number is currently unavailable. We are sorry if this incident disrupted our service for customers.
"Police investigations are ongoing."
A Durham Police spokeswoman said: "The police investigation into the source of the envelope and the nature of the powder will continue."