Speaker Emerita Nancy Pelosi’s district office received a suspicious letter containing an unknown substance, her office said Wednesday. The mailing prompted a federal investigation, and her office said everyone was safe.

More than three dozen Republican and Democratic lawmakers nationwide have received envelopes containing white powder. Pelosi’s office said its staff were following established security procedures.

Rep. Kevin Mullin said Tuesday that his office received mail containing white powder. His staff reported it to law enforcement after following procedures for suspicious mail. Similar letters were sent to Bay Area Reps. Jimmy Panetta, Zoe Lofgren and Mark DeSaulnier.