Congresswoman Gwen Moore is among several elected officials across the country who have received suspicious mail containing an unknown substance.
The Milwaukee Democrat confirmed that a letter was delivered to her office.
Moore said staff members followed established safety procedures, and the office will no longer sort mail on-site.
Similar letters were sent to Minnesota Senator Amy Klobuchar, Minnesota’s Secretary of State, and five lawmakers in the Chicago area.
The FBI and U.S. Postal Inspection Service are investigating the incidents.
