Federal authorities are investigating a series of suspicious letters containing unknown substances that have been sent to election offices and congressional offices across the United States. The probe involves the FBI, U.S. Postal Inspection Service, and U.S. Capitol Police, who have urged recipients to treat the mailings as potentially hazardous.

The investigation came to light through communications sent to Senate offices indicating that law enforcement agencies are actively working to intercept additional letters, although some may have already reached their destinations. The threat has primarily affected Senate offices, but officials in the House of Representatives have also been monitoring the situation.

Several election offices in states such as Louisiana and Oklahoma were evacuated earlier this week after receiving packages containing powdery substances. Multiple states reported that these suspicious letters were either received by or intercepted before reaching their election offices. Among those targeted was the office of Senator Alex Padilla of California, where a letter containing a suspicious substance was intercepted by the U.S. Postal Service.

The Postal Inspection Service has emphasized its commitment to protecting election officials from threatening and dangerous mail. Brendan Donahue, deputy chief inspector of the Postal Inspection Service, described any threat toward election officials as unacceptable and confirmed ongoing investigative efforts.

This incident occurs as the nation prepares for the November 3 midterm elections, which will determine control of Congress and other key offices. The U.S. Postal Service announced earlier in October that it has implemented enhanced measures to handle the expected volume of mail-in ballots, including extended hours at some retail locations, expedited handling, extra deliveries, and special pickups. These efforts aim to ensure timely processing of ballots during the final days of the election season.

Postmaster General David Steiner affirmed USPS readiness to manage millions of ballots and detailed new protocols starting October 24 to expedite completed ballots to election offices. These protocols include bypassing standard processing steps when necessary to guarantee on-time delivery.

The heightened focus on mail security follows regulatory developments earlier in the year. In March, former President Donald Trump issued an executive order seeking stricter controls on mail-in ballots, but the U.S. Supreme Court blocked a USPS rule that would have enforced such measures. The blocked rule would have required states to provide voter lists to the Postal Service and use agency-approved ballot envelopes with unique barcodes, allowing USPS to reject ballots not complying with these standards.

In the 2024 presidential election, the Postal Service handled 99.2 million ballots, with approximately 30% of voters casting ballots by mail—down from 46% in 2020. Authorities continue to investigate the suspicious mailings as part of broader efforts to secure election-related processes and protect officials during the critical upcoming elections.