In the memo, Assistant City Attorney Paul Cooper tells Chief of Staff Lee Burdick that her quizzing of the staff is inappropriate and is interfering with the work of city attorneys, U-T San Diego reported.
The memo also calls on Burdick to hand over certain documents that she has been withholding, citing attorney-client privilege.
"Your inappropriate use of this non-existent privilege now places the city in the untenable position of not being able to carry out its legal obligations therefore subjecting the city to potential liability," the memo said, according to U-T.
While Burdick is an attorney, the memo goes on to explain that the only attorney that serves the city of San Diego is the city attorney, and Burdick will be sued if she doesn't comply.
The memo tells Burdick, "you are a witness in this litigation, not an attorney." The word "witness" is underlined.
Calls seeking comment from the mayor's office were not returned.
Filner is facing allegations of unwanted advances from at least eight women, including his former communications director, Irene McCormack Jackson, who filed a lawsuit July 22 against the mayor and the city. In the lawsuit, McCormack alleges Filner asked Jackson to work without panties, demanded kisses, told her he wanted to see her naked, and dragged her in a headlock while whispering in her ear.
The City Council voted unanimously Tuesday to sue Filner to require him to pay for any damages or attorney fees out of his own pocket if the city is held liable. It also moved to deny Filner funds for his legal defense.
Filner's attorney Harvey Berger had argued in a letter to the city attorney that the city should pay the mayor's legal fees because it didn't provide him with state-required sexual harassment training.
Berger said the city's trainer canceled the session and did not reschedule, but a former Filner staffer contracted that Thursday.
Jay Goldstone, Filner's interim chief operating officer, said it was the mayor, not a city trainer, who canceled the training briefing.
Berger did not immediately return an after-hours message seeking comment.
Filner, who is 70 and divorced, has pledged to enter two weeks of "intensive" therapy Aug. 5, defying calls from his own party leaders to resign. The former 10-term congressman is less than eight months into a four-year term. He is San Diego's first Democratic mayor in 20 years.