Ill. Admin. Code tit. 86, § 850.115
a) Municipality, County, and Third Party Participation.
4) Tax compliance referrals may be made only by a municipality, county, or third party and shall be made in the form and manner required by the Department, including any requirement that the referral be submitted electronically. The tax compliance referral shall, at a minimum, include:
C) engaging in collection actions against any taxpayer for the tax; or
b) Department Participation.
A) the Department has previously conducted an audit;
3) If the Department determines that the referral is actionable, then it shall determine whether the taxpayer is currently under audit or scheduled for audit by the Department. If the taxpayer is not currently under audit by the Department or scheduled for audit by the Department, the Department shall determine whether it will schedule the taxpayer for audit.
B) if the taxpayer is not under audit or scheduled for audit, and the Department schedules the taxpayer for audit, it shall provide notice to the taxpayer pursuant to established audit procedures. The reasons why the Department may decide to retain an actionable referral for audit by the Department includes, but are not limited to, the following:
4) If the Department notifies the taxpayer as provided in subsection (b)(3)(B), the notice shall include, but not be limited to, the following:
6) After the conducting of a certified audit by a qualified practitioner, and upon receipt of a qualified practitioner’s report made on behalf of a participating taxpayer, the Department shall do the following:
c) Qualified Practitioner Participation.
1) The scope of the qualified practitioner's sales and use tax compliance review may include only the following:
D) whether the proper tax rate was charged;
2) A qualified practitioner is responsible for the following:
6) After completion of the certified audit, the qualified practitioner must submit to the Department a report of the certified audit made on behalf of a participating taxpayer. The Certified Audit Report submitted for review must include:
d) Taxpayer Participation.
3) To participate in the audit, the taxpayer must:
The Department shall complete its evaluation of all audit referrals under subsection (a) within 90 days after receipt of the referral and shall handle all audit referrals as follows: