220 ILCS 35/3
No utility supplier which provides utility service shall request a deposit from any small business, for any reason, in excess of 1/6 of the estimated annual charges for service for that small business computed at the net rate for that class of service.
A utility may request a minimum amount equal to 1/3 of a requested deposit to be paid within 12 days after the issue date of a notice requesting such deposit. A utility may require the full payment of the remaining balance of the deposit be paid by the applicant no sooner than 2 billing periods typically or routinely used by the utility.
The date by which the entire deposit must be paid shall be plainly indicated on the notice of deposit request. The amount of the deposit may be adjusted at the request of the applicant or utility at any time when the character or degree of use of the utility service materially changes or when it is clearly established that the character or degree of use of the service will materially change in the immediate future.
220 ILCS 35/3