A suspicious, white powdery substance turned up in two letters to Rep. Norma Torres’ Ontario district office on Wednesday, July 24, she said.

Interns and staffers discovered the letters, prompting hazmat teams to descend on the site, where they were investigating.

Torres, who described the incident as an “attack,” said out of caution, her staff was remaining on site “until more information is found.”

In a statement, Torres said no one was experiencing any symptoms, potentially from the powder, and that U.S. Capitol Police and local law enforcement have been notified.

“Out of an abundance of caution, my staff will be sheltering in place until local law enforcement determines the nature of the substance and will follow their guidance on the next best course of action,” Torres said.

Torres’s district office is in Ontario, but the district spans from Fontana to Chino to Pomona.