An Internal Revenue Service building in Kentucky has been sealed off after a letter containing an unknown white substance was received.
Hazardous materials experts are investigating after workers reported the suspicious sticky substance in an envelope that had been handled by several people.
Emergency workers brought one woman out of the building and began scrubbing her down.
They then removed her clothes, wrapped her twice in plastic and took her to hospital for further decontamination and observation.
The Cincinnati Enquirerreports 3,500 people are employed at the office in Covington.
It says officials placed the suspicious letter in a can which was driven to a Hamilton County Sheriff's Office helicopter and flown away.
IRS spokesman Mr Chris Kerns says the building, which can also have up to 188 children in its childcare facility, is in "standard procedure lockdown".
The centre, which processes 20 million individual and business tax returns from seven states, has had about 20 similar incidents in the past five years.
The incident comes a day after six people were hosed down by hazardous materials crews at a doctor's office in Montgomery Road in Sycamore Township after a suspicious package was delivered.
PA