Cal. Pub. Util. Code § 12131

The incumbents of permanent positions who have held such positions for a period of at least six months continuously next preceding the time that a civil service system is first adopted shall be continued in their positions as if appointed thereto after examination and certification from a list of eligibles, and shall be governed thereafter by this division and the rules and regulations adopted pursuant thereto but shall not be subject to the six months’ probation period.