220 ILCS 30/10.6
3 shall be paid to the Commission on or before the thirtieth day of January following the end of the calendar year subject to tax. However, for the tax period July 1, 1981 through December 31, 1981 the amount of tax due under Section 10.3 shall be paid to the Commission on or before February 1, 1982. In the event that an adjustment in the amount of tax due should be necessary as a result of the filing of an amended return pursuant to Section 10.5, the amount of any deficiency shall be paid by the electric supplier together with the amended return. Any excess tax payment by the electric supplier shall be returned to the supplier after filing a claim for credit, in the form of a credit memorandum in the amount of such excess. However, if such deficiency or excess is less than $1, then the electric supplier need not pay the deficiency and may not claim a credit.
220 ILCS 30/10.6