Employees at the B- Well Chiropractic on Brainerd Road say they opened two letters and a powdery substance fell out.
They say their fingers and hands were burned.
Firefighters and police evacuated the business.
A Haz-mat team collected the letters, powder, and the employees clothes in a special evidence container.
The women were decontaminated and checked out by paramedics who appeared to be uninjured.
Initial testing indicated it was not a serious threat.
The FBI and U.S. Postal Service will handle the investigation.