Ill. Admin. Code tit. 92, § 3280.1090
a) When the Department has reason to believe that a person is engaging in conduct which involves a violation of any provision of the MCSR, the Department may issue a warning letter which shall:
b) The warning letter shall be served in the manner prescribed in Section 386.1020.
(Recodified from 92 Ill. Adm. Code 386 (Department of Transportation) pursuant to P.A. 104-0025, at 49 Ill. Reg. 12543)