CA Elec Code Section 20501

(a)

A candidate or state measure proponent is liable for any slander or libel committed by a committee that is controlled by that candidate or state measure proponent as defined by Section 82016 of the Government Code if the candidate or state measure proponent willfully and knowingly directs or permits the libel or slander.

(b)

A person who is a sponsor of a sponsored committee, as defined by Section 82048.7 of the Government Code, is liable for any slander or libel committed by the sponsored committee if the sponsor willfully and knowingly directs or permits the libel or slander.