Speaking to reporters after a news conference on an unrelated subject, Quan accused Russo of having "his own political agenda" by issuing a five-page letter to her stating that having Siegel give advice to Quan and other city officials could create legal problems for the city.
"The problem is that John Russo tends to attack by press release," Quan said, and complained that he issued his letter last Friday while she was still in Washington, D.C., where she attended U.S. Conference of Mayors meetings and also met with White House officials.
But Russo said a copy of his letter was hand-delivered to Quan's office on Friday and that he always makes his opinions on city charter issues available to the public by posting them on his office's website.
Quan, who has known Siegel since they met at the University of California at Berkeley in 1968, said she interprets Russo's opinion as saying that she can't get legal advice from anyone other than Russo.
"That's ridiculous," she said. "That's not right."
Russo said Quan can and should seek advice from anyone she wants, but there are two problems with Siegel acting as a legal adviser for her as mayor and for other city officials.
Russo said the first problem is that Siegel and his son are opposing in court his attempt to get an injunction that would crack down on alleged illegal activity by the Nortenos gang in Oakland's Fruitvale District.
In his letter, Russo alleged that Siegel has a conflict with the city because he is representing alleged gang members and has "an adversarial relationship with the city."
He warned Quan that if she talks to Siegel about the litigation, "There are significant risks associated with communications between you and attorney Siegel due to his conflict of interest."
Russo said the second problem is that any legal advice that Siegel provides to city departments heads, such as Police Chief Anthony Batts, wouldn't be protected by the attorney-client privilege because the city attorney is the only legally recognized lawyer for the city.
Any legal advice that Siegel provides to city officials would have to be disclosed to opposing counsel, and that could cause problems for the city, Russo said.
He said Siegel could also put department heads "in an impossible situation" by giving them legal advice that they might feel obliged to comply with because Siegel is acting on Quan's behalf and they all work for Quan.
Russo said he believes the problem is that Quan doesn't understand the separation of powers between the city attorney's and mayor's offices even though she served on the City Council for eight years before becoming mayor on Jan. 3.
"She has to clear up the confusion," and let department heads know that they shouldn't discuss the city's legal issues with Siegel, he said.
He wrote in his letter to Quan, "Violation of the city charter is a crime. It is now incumbent upon you to uphold your oath to defend the charter."