A hazmat crew in Los Angeles investigated the office of California Rep. Maxine Waters due to a "suspicious package" left there that was labeled "anthrax," according to the Los Angeles Fire Department.
The fire department later tweeted that no hazardous materials were found and that no one required hospitalization.
Waters, 79, became engulfed in a feud with President Donald Trump last month after she called on her supporters to publicly confront and harass members of the Trump administration in response to the zero-tolerance immigration policy that led to thousands of children being separated at the U.S. border.
Days later, Waters clarified her call to action after Trump claimed that she "called for harm" towards his supporters.
"I believe in peaceful, very peaceful protests," Waters told reporters in June. "I have not called for the harm of anybody. This president has lied, again, when he's saying that I've called for harm."
Last week, Waters warned her supporters of potential "armed protests" against her after an extremist group called for ongoing demonstrations outside her Los Angeles office.
The longtime congresswoman advised her supporters against being "baited" into counter-demonstrations with the "Oath Keepers," a group she described as "an anti-government militia" that has staged armed protests across the country.
The Oath Keepers has a track record of "violent and provocative behavior," Waters wrote on Facebook last week.
On Thursday, the officers and personnel from the Los Angeles Police Department were on site at Waters' office "to ensure safety and security," she wrote.
"My primary concern is to maintain the safety and security of the protesters, staff, and constituents of California’s 43rd Congressional District -- a task that would be exceedingly complicated by large crowds of protesters and counter-protesters," she said.
ABC News' Karma Allen and Marilyn Heck contributed to this report.