Law enforcement authorities are investigating an anthrax scare at the offices of Rep. Jo Bonner (R) and several other Alabama lawmakers.

Bonner's offices were closed on Monday after each received suspicious letters, according to a spokesman for Bonner, while the offices of Rep. Bobby Bright (D) and Sens. Richard Shelby (R) and Jeff Sessions (R) were also targeted, according to the Associated Press.

Gazmat crews are on the scene at two of Bonner's district offices, in Mobile and Foley, Ala., according to a local CBS affiliate.

The letters were received this morning, Bonner's spokesman said, and the letters have been turned over to law enforcement. The offices haven't yet begun to reopen. 

The AP said that the powder in the envelopes has been confirmed as not being anthrax, though authorities are uncertain what the substance is. The AP also reported that federal investigators suspect the letters came from the same source.

The Washington offices Sens. Tom Daschle (D-S.D.) and Patrick Leahy (D-Vt.) were targeted in live anthrax attacks in the fall of 2001. Anthrax scares have popped up occasionally with lawmakers in the years since.

This post was updated at 3:40 p.m.