A white powder was found in a stack of mail by a staffer in Meeks's office, according to the lawmaker's Chief of Staff Sophia Lafargue. The substance was found in a stack of envelopes, but its origin wasn't clear, Lafargue said.

Meeks's office immediately called the Capitol Police when the substance was found. 

Lafargue said the powder was found sometime around noon.

This incident follows multiple mailings of ricin, a deadly poison made from castor beans, to a number of elected officials, including Sen. Roger WickerRoger WickerOvernight Defense: GOP chairman moves ahead with 0B defense bill | Lawmakers eye 355 ship navy | Senate panel seeks answers on shoot down of Syrian jet Lawmakers unveil bill to set 355-ship Navy Overnight Tech: Uber CEO resigns | Trump's Iowa tech trip | Dems push Sessions to block AT&T-Time Warner deal | Lawmakers warned on threat to election systems | MORE (R-Miss.) and President Obama.

Since the ricin-laced letters were discovered, the FBI has been investigating.

Over the weekend law enforcement charged James Everett Dutschke with sending the letters. Dutschke was arrested Saturday by federal marshals.