The FBI is investigating a threatening letter containing white powder that was delivered to the "Dancing With the Stars" production office at CBS Studios on Friday.
"An initial field screening was negative for hazardous substances, but the letter will be transported to a regional lab for further testing," FBI spokeswoman Laura Eimiller said.
CBS Station KCBS correspondent Suzanne Marques confirmed that a powdery substance was inside a threatening letter received at Bungalow One on the studio lot.
Sources told Marques the threatening letter was sent to contestant Bristol Palin criticizing a recent performance.
Hazardous materials officials with the city of Los Angeles, the Los Angeles Fire Department, Los Angeles Police Department and the FBI responded to the CBS Studios lot where the hit ABC show is staged, authorities said.
In a statement, ABC confirmed the envelope was received at the show's production office, and that the substance was determined to be talcum powder.
The FBI and LAPD are conducting a joint investigation, Eimiller said. She would not say to whom the letter was addressed.
The incident occurred just days before the final showdown for the mirrorball trophy.
Palin, Jennifer Grey an dKyle Massey will compete for the prize next week.
The show has made headlines in recent days because of an outcry by some who believe that political supporters of Sarah Palin may be manipulating the voting system. Bristol Palin has remained on the show, despite consistently landing at the bottom of the judges' leaderboard.