Cal. Code Regs. tit. 18 § 18530
Where the amount shown as the tax by the husband and wife on a joint return made under Revenue and Taxation Code Section 18522 exceeds the aggregate of the amounts shown as tax on the separate return of each spouse, and such excess is attributable to negligence, intentional disregard of rules and regulations, or fraud at the time of the making of such separate returns, there shall be assessed, collected, and paid in the same manner as if it were a deficiency, an additional amount as provided in the two succeeding sentences. If any part of such excess is attributable to negligence, or intentional disregard of rules and regulations at the time of the making of such separate return, but without any intent to defraud, this additional amount shall be 20 percent of the total amount of the excess. If any part of such excess is attributable to fraud with intent to evade tax at the time of the making of such separate return, this additional amount shall be 75 percent of the total amount of the excess. The above additions are in lieu of the additions to the tax provided in Revenue and Taxation Code section 19164, subdivisions (a) and (c).
Cal. Code Regs. Tit. 18, § 18530