Just days before an apparent attack on “Empire” star Jussie Smollett earlier this week, a letter containing white powder was sent to the show’s set in Chicago, prompting a response from the HAZMAT unit, CNN reports.

The report cites Chicago police spokesman Anthony Guglielmi saying the letter was received Jan. 22 at Cinespace Studios, where the Fox show is filmed.

“Guglielmi said authorities determined the powder to be aspirin, but declined to give details on the content of the letter,” CNN reports. “The FBI is leading the investigation into the letter, he added.”

As we reported previously, Smollett also received a threatening letter containing racially charged and homophobic language a few days before he was reportedly attacked by two assailants in the early-morning hours on Jan. 29.