Letters containing a white powdery substance have been sent to Sen. Marco Rubio and other Florida senators.
Investigators are looking into whether there is a link.
A Jacksonville Sheriff's Office bomb squad was called to Rubio's office on Tuesday after two Rubio staff members discovered a powdery substance in a letter.
The building was evacuated and two people were evaluated before the substance was deemed safe. Rubio was in Washington.
On Monday, Democratic Sen. Bill Nelson's office was evacuated after staff found a powdery substance inside a threatening letter.
Nelson was in Jacksonville for a fundraiser but had already left his office when the substance was discovered. The powder turned out to be corn starch.
FBI spokesman Jeff Westcott tells The Florida Times-Union that the agency's Jacksonville office is investigating the mailings.
This is based on a story by The Associated Press.