The Hillsborough County Sheriff's Office and FBI Tampa Division are investigating a threatening letter with a suspicious white, powdery substance sent to the Mosaic headquarters in Lithia, near Brandon.
The letter was received Friday.
Hillsborough deputies and Tampa FBI agents were on scene, conducting an investigation at the phosphate company's headquarters Friday night.
The envelope containing the white powdery substance is being analyzed at the FBI laboratory. Results are expected to take several days.
Authorities are asking anyone with information about the investigation to contact the Tampa FBI at (813) 253-1000.