From and after January 1, 1970 any employee who is credited with 35 or more years of contributing service may elect to discontinue the salary deductions for all annuities as specified in Sections 9-133, 9-170, and 9-176. Upon such election the annuity for the employee and his wife or widow is fixed and determined as of the date of such discontinuance. No increase in annuity for the employee or his wife or widow accrues thereafter while he is in service. This election shall be in writing to the Retirement Board at least 60 days before the date the salary deductions cease.
40 ILCS 5/9-170.1