Cal. Rev. & Tax. Code § 18642

(a) All owners and transferors of an interest in real property or a mobilehome shall file a return upon written request by the Franchise Tax Board which includes a social security number or other identification number prescribed by the Franchise Tax Board, identification of the property interest, and any other pertinent information about the interest requested by the Franchise Tax Board.
(b) Subdivision (a) shall not apply to any of the following:
1. (1) Property granted a homeowner’s property tax exemption.
2. (2) Property which is not assessed by a California county assessor.
(c) Owners and transferors failing to file a return required by subdivision (a) on or before the due date of the return shall be subject to the penalty provided by Section 19183, unless the failure is due to reasonable cause and not due to willful neglect.
(d) Owners failing to file a return required by subdivision (a) within 60 days of the due date of the return shall be subject to the sanctions provided by Section 17299.9 disallowing certain expenses related to the property for which a return is required, unless it is shown that the failure is due to reasonable cause and not due to willful neglect.
(e) The Franchise Tax Board shall mail to each owner and transferor required to file a return pursuant to subdivision (a) a notice at least 60 days prior to the due date of the return. The notice shall be in a form and shall include any information which the Franchise Tax Board prescribes and shall advise owners and transferors of all of the following:
1. (1) The requirement to provide the Franchise Tax Board with a social security number or other identification number prescribed by the Franchise Tax Board.
2. (2) When the statement is due.
3. (3) A general description of the tax consequences of not providing the requested information.
(f) The social security number or other identification number furnished pursuant to this section shall be used exclusively for tax administration purposes. It is the intent of the Legislature in enacting this section to utilize the social security number or other identification number for the sole purpose of establishing the identification of individuals or entities affected by state tax laws.