A letter with an “unknown substance” was reportedly sent to Senator Susan Collin’s Portland office Friday.

The letter was intercepted with no injuries, and law enforcement is investigating the situation.

A separate letter was also mailed to Collins’ Washington, DC, office but was intercepted by US Capitol Police.

The Associated Press reports “suspicious substances” have been mailed to congressional and election offices nationwide in the past several days.

According to the AP, an FBI statement said the bureau and the Postal Inspection Service were “investigating a series of suspicious mailings sent to various addresses nationwide, including Secretary of State offices and their related election offices.”

“Some of the letters contained an unknown substance and we are working closely with our law enforcement partners to respond to each incident,” the AP reported the statement read. “We are also working with our partners to identify the individual or individuals responsible for the letters.”

Collina is locked in a tight and contentious reelection race against Democrat Troy Jackson. The contest is receiving outsize nation attention because it could possibly determine control of Congress in November’s election.