Torres, D-Ontario, says while there were no injuries or illnesses reported, her staffers at the district office are sheltering in place until the substance can be analyzed.
"Hazmat teams are on site investigating the substance and my staff are remaining in place until more information is found," Torres wrote on X. "No one is experiencing any symptoms at this time, and all normal operating precautions were observed, including the use of airtight equipment while opening the letters."
Capitol Police and local law enforcement are also investigating.
Torres has represented California's 35th congressional district since 2015.
Information about who may have sent the letters - and whether both came from the same source - was not immediately disclosed.
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