You don't have to be an attorney to read a Court decision.

This case covers Oregon public employee retirement law from 1940 through 1996 when the voters tried to get rid of the 6% pickup and most of the rest of PERS.

Retirement Cases decided in 1940, 1966, 1971, 1974, 1975, 1978, 1980 are cited and point to this result:

"The enactment of the PERS scheme in 1953 created constitutionally protected rights in PERS members.  PERS constitutes an offer by the state to its employees for a unilateral contract that may be accepted by the tender of part performance by those employees.   The PERS pension plan becomes vested in the state's employees on acceptance of employment.   The six percent pick-up, guaranteed rate of return, and sick leave credit are integral terms of plaintiffs' PERS pension contracts; they also are contractual obligations of the state under plaintiffs' PERS contracts."

State Police v. Oregon (1996)

http://law.justia.com/cases/oregon/supreme-court/1996/323-or-356.html