820 ILCS 105/2
The General Assembly finds that the existence in industries, trades or business, or branches thereof, including offices, mercantile establishments and all other places of employment in the State of Illinois covered by this Act, of conditions detrimental to the maintenance of the minimum standard of living necessary for the health, efficiency and general well-being of workers, leads to labor disputes, and places burdens on the State, and all other subordinate political bodies thereof, to assist and supply necessary moneys and goods to workers and their families to aid them to exist on a minimum budget for their needs, and thus places an unnecessary burden on the taxpayers of this State. Therefore, it is the policy of this Act to establish a minimum wage standard for workers at a level consistent with their health, efficiency and general well-being; to safeguard such minimum wage against the unfair competition of wage and hour standards which do not provide such adequate standards of living; and to sustain purchasing power and increase employment opportunities.
It is against public policy for an employer to pay to his employees an amount less than that fixed by this Act. Payment of any amount less than herein fixed is an unreasonable and oppressive wage, and less than sufficient to meet the minimum cost of living necessary for health. Any contract, agreement or understanding for or in relation to such unreasonable and oppressive wage for any employment covered by this Act is void.
820 ILCS 105/2