California Code, Revenue and Taxation Code - RTC § 11655

(a) Except as provided herein, all information and records relating to the business affairs of persons required to report to the board pursuant to this part shall be held secret by the board.

(b) The board shall disclose information and records to law enforcement agencies, grand juries, and other duly authorized legislative or administrative officials of the state pursuant to their authorization to examine such information and records.

(c) The board also may disclose information, records, and appraisal data relating to state assessment of private railroad companies whose cars operate in interstate commerce to tax officials of other states having duties corresponding to those described by this part.  The disclosure shall be limited to instances in which there is a reciprocal exchange of information by the states in which the cars operate, and shall be made only pursuant to a written agreement between the agencies involved.  The agreement shall provide that any request for information be in writing, shall specify the information to be exchanged, and shall require that any information furnished be used solely for tax administration purposes and otherwise shall be held secret.  The request for information and any written material furnished pursuant to the request shall be open to inspection by the person to whom the information relates at the office of the board in Sacramento.