At 12:20 pm last Tuesday, an official in the Louisiana secretary of state’s office opened a mailed letter and white powder fell out. The office was immediately evacuated and the employee was rushed to the emergency room. The employee was not injured and subsequent tests showed that the substance was not harmful. By Wednesday, the office was back open.

“Tuesday’s event did not impact any election operations in preparation for the upcoming election,” Trey Williams, a spokesperson for Louisiana’s secretary of state, tells WIRED.

But the incident was not isolated. A WIRED investigation has found that over the course of the following days, election offices in at least 31 other states were targeted with similar letters as they prepared for the midterms that are now just two weeks away. Many of the states have made public statements acknowledging the receipt of these letters, but WIRED’s accounting of all the incidents shows the full scale of this campaign for the first time.

The vast majority of letters were intercepted by the United States Postal Service before they reached their intended targets, state officials tell WIRED, but in Arizona, Delaware, Oklahoma, South Carolina, and Louisiana the letters were not intercepted, leading to election offices being evacuated when white powder was discovered.

The states that confirmed receipt of a letter are: Alaska, Arizona, California, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Kansas, Louisiana, Maine, Maryland, Massachusetts, Minnesota, Mississippi, Nebraska, New Hampshire, New Mexico, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Utah, Virginia, Washington, Wisconsin, and Wyoming.

Election officials in 10 states—Vermont, Michigan, New York, Rhode Island, Texas, West Virginia, Colorado, Kentucky, Indiana, North Carolina—and DC tell WIRED they have not received any suspicious packages. The eight remaining state election offices did not respond.

The white powder contained in the letters that have been opened so far has been reported as not harmful, but election offices remain on high alert.

“We are deeply concerned by these incidents,” the National Association of Secretaries of State and the National Association of State Election Directors wrote in a joint statement. “As we have each stated in the past, threats against election officials and workers have no place in our democracy. Those who administer our elections should never fear for their safety while carrying out their essential duties.”

As news of the letters being sent emerged last week, federal agencies alerted other election offices in some states that a potentially dangerous package was on the way. The FBI notified authorities in Alaska on Friday that an envelope was expected to arrive the following day. At about 9 am Saturday morning, the USPS identified the suspicious package, the Juneau Independent reported.