The U.S. Capitol Police suspended an officer after anti-Semitic reading material was "discovered near his work area," the department said on Monday.
The Washington Post, which first reported the story, said a congressional aide saw a printed copy of "The Protocols of the Meetings of the Learned Elders of Zion" at a checkpoint inside the entrance of a congressional office building.
The tract, originally published in the early 20th century, is described by the Anti-Defamation League as "a classic in paranoid, racist literature."
The officer is suspended pending an internal investigation.
"We take all allegations of inappropriate behavior seriously. Once this matter was brought to my attention, I immediately ordered the officer to be suspended until the Office of Professional Responsibility can thoroughly investigate," said Acting Capitol Police chief Yogananda Pittman in a statement.
Scrutiny on U.S. Capitol Police has been high since Jan. 6, when hundreds of supporters of former President Donald Trump stormed the building and overpowered Capitol Police officers in a bid to block the certification of President Joe Biden's victory.
Congressional and law enforcement investigators are looking into the January events while Capitol Police are performing an internal investigation into the conduct of 35 officers during the riot.