Mayoral candidate Jeff Adachi publicly urged the Justice Department to investigate actions by a political group that supports Lee's campaign.
It stems from home video taken Friday in Chinatown that shows workers wearing "Ed Lee for Mayor" shirts supposedly marking ballots for voters.
Adachi, and six other of Lee's challengers, want the California Secretary of State to send election monitors immediately to San Francisco to investigate the irregularities.
Lee spoke to ABC7 News late Monday and said he's disturbed by the actions of some independent groups supporting him. He condemned any type of tampering with voter's ballots.
"They should never be intimidated to vote for anybody," Lee said. "If there is anyone out there that thinks they are representing me, I want them to cease and desist."
Lee reiterated the group that organized the Chinatown event, the SF Neighbor Alliance, is not affiliated with his campaign. He says he supports a review of the activities captured on video.
