40 ILCS 5/14-112
A covered employee who retires from service prior to the age of becoming eligible for old age insurance payments under the Federal Social Security Act and who at the time of retirement is fully insured under that Act, may elect to have the retirement annuity increased prior to such eligible age and reduced after such age by amounts which have equivalent actuarial values. Such modification is for the purpose of coordinating a member's retirement annuity with old age insurance benefits receivable under that Federal Act.
However, the option under this Section is not available if the resulting payments by the System after the employee becomes eligible for old age insurance payments under the Federal Social Security Act would be less than $10 per month.
40 ILCS 5/14-112