A California congressional office has been swept into a growing national investigation involving suspicious mail after a staff member discovered an envelope containing white powder.

Democratic Rep. Jimmy Panetta said Friday that the envelope arrived at his Santa Cruz district office while an employee was carrying out her regular morning work responding to constituents.

According to Panetta, the staffer noticed the powder, placed the envelope in a trash can, evacuated her colleagues from the office and contacted 911.

Panetta said protecting his employees remained his foremost concern. Medical personnel initially cleared the staff member and the other workers who had been in the office.

Panetta said the apparent intimidation attempt would not stop his office from carrying out its responsibilities.

He added that his team would continue serving residents of California’s 19th Congressional District and standing behind the country’s democratic institutions.

Panetta’s office said the envelope had been mailed from New York and appeared to match other letters currently under federal investigation.

Because the envelope was opened and then quickly thrown away, officials were unable to verify the precise return address, the office said.

The episode comes as the FBI, the US Postal Inspection Service and US Capitol Police examine a series of suspicious letters sent to congressional and election-related offices across the country.

A notice circulated among Senate offices said investigators were attempting to stop additional mailings, while acknowledging that some suspicious letters might still be delivered.

The alert featured an image of one envelope bearing the postmark “DSA” and a New York City return address once used on membership forms by the Democratic Socialists of America.

The group said it has not occupied that location since 2013.

In California, Democratic Rep. Zoe Lofgren and Independent Rep. Kevin Kiley also said they had received suspicious mail. Democratic Sen. Alex Padilla said the Postal Service intercepted a suspicious package addressed to his office before it arrived.

Other lawmakers nationwide who reported suspicious mail included Reps. Seth Moulton, Maxwell Frost, Darren Soto, Ritchie Torres and Bonnie Watson Coleman, as well as Sens. Mike Rounds, Chris Murphy, Lisa Blunt Rochester, Chris Coons, Kirsten Gillibrand and Amy Klobuchar.

In a separate incident, deputies responded to a report of potentially hazardous material at the Santa Cruz County Government Building on Ocean Street. The building was evacuated as a precaution, and no injuries were reported.