The Alameda County Fire Department's Hazardous Material Team responded to four reports of white powder found at local law enforcement headquarters, Friday.
In each case, legal-sized white envelopes containing a suspicious white powdery substance arrived via mail.
The first call came in at 10:14 a.m. from the Hayward Police Department and similar calls followed from police departments in San Leandro, Union City and Berkeley. It is still unknown if any other agencies received a similar envelopes.
The substances found in Hayward, San Leandro and Berkeley were deemed non-hazardous, while the scene in Union City is still under investingation.
The FBI is assisting local law enforcement agencies with their investigation, according to spokesperson Julie Sohn.