Sec. 5.07. OUTSIDE INCOME PENSION REDUCTION. (a) The board shall require each disability retiree retiring after August 29, 1979, to provide the board annually not later than May 1 of each year with a true and complete copy of the retiree's income tax return for the previous year, except for a retiree who is 65 years of age or older as of December 31 of the previous year.

(b) If the retiree received income from other employment, including self-employment, during the preceding year, the board may reduce the retiree's disability retirement annuity by the amount of $1 for each month for each $2 of income earned by the retiree from the other employment during each month of the previous year, except that the disability retirement annuity may not be decreased below the amount determined under Section 5.05(c) of this Act.