Ill. Const. art. IV, § 10

The General Assembly shall provide by law for a uniform effective date for laws passed prior to June 1 of a calendar year. The General Assembly may provide for a different effective date in any law passed prior to June 1. A bill passed after May 31 shall not become effective prior to June 1 of the next calendar year unless the General Assembly by the vote of three-fifths of the members elected to each house provides for an earlier effective date. (Source: Amendment adopted at general election November 8, 1994.)