Is a city employee entitled to a vested contractual right to earn a pension?

However, obtaining a vested contractual right to earn a pension upon acceptance of public employment does not mean that all terms governing the pension system then in effect become vested contractual rights of the employee. "[A]n employee may acquire a vested contractual right to a pension but ... this right is not rigidly fixed by the specific terms of the legislation in effect during any particular period in which he serves." ( Kern v. City of Long Beach (1947) 29 Cal.2d 848, 855[179 P.2d 799] .) Thus, we must analyze "[t]he nature and extent of the city's obligation" as ascertained from the language of the pension provisions and the judicial construction of similar legislation. ( Id. at p. 850, 179 P.2d 799 .)