35 ILCS 1010/1-80: Representation.

(a) Appearances in proceedings conducted by the Tax Tribunal may be by the taxpayer or by an attorney admitted to practice in this State. The Tax Tribunal may allow an attorney who is not admitted to the practice of law in Illinois by unlimited or conditional admission, but who is authorized to practice or licensed in another state, territory, or commonwealth of the United States, the District of Columbia, or a foreign country to appear and represent a taxpayer in proceedings before the Tax Tribunal for a particular matter as provided in Illinois Supreme Court Rule 707.

(b) The Department of Revenue shall be represented by the Attorney General in all proceedings before the Tax Tribunal.