40 ILCS 5/19-201
The board of directors of public libraries organized under an Act of the General Assembly of the State of Illinois, entitled "An Act to authorize cities, incorporated towns and townships to establish and maintain free public libraries and reading rooms", approved and in force March 7, 1872, and maintained thereunder in cities having a population exceeding 500,000 inhabitants shall have power and it shall be its duty to create a public library employes' pension fund, which shall consist of amounts retained from the salaries or wages of employes, as hereinafter provided, which amounts shall be deducted in equal monthly installments from such salaries or wages at the regular time or times of the payment thereof, all fees or penalties collected for retention of books beyond the time prescribed by rule of the board of directors by virtue of by-laws, rules and regulations adopted under authority of Section 5 of the Act herein referred to by its title and such other moneys derived from miscellaneous sources as the board of directors shall determine.
40 ILCS 5/19-201