A letter containing fentanyl was mailed to the elections office in Fulton County, Georgia, Secretary of State Brad Raffensperger said during a press conference Thursday. “We became aware of the situation that there is actually still an envelope that is traveling in the mail and headed towards Fulton County,” Raffensperger said, adding that he lost his own son to fentanyl five years ago. “We know how deadly this stuff is.” He labeled the act “domestic terrorism” and his office later released a statement detailing their efforts to protect election workers. “We’re working with our state and federal partners to determine if any additional Georgia officials are being targeted,” the secretary of state’s office said in the statement. “We will work tirelessly to ensure that Georgia elections remain free, fair, and secure.” Both the U.S. Postal Inspection Service and the Federal Bureau of Investigation are investigating the letters sent to various states’ election workers, according to MSNBC. The threatening letter comes after four other elections offices in Washington were evacuated due to suspicious letters, two of which authorities said contained fentanyl, the Associated Press reported.