UIC §1086: (a) Each employing unit within 15 days after becoming an employer as defined in this part shall register with the department on a form prescribed by the department.

(a) Each employing unit within 15 days after becoming an employer as defined in this part shall register with the department on a form prescribed by the department. (b) (1) Notwithstanding subdivision (a), an Indian tribe (as described by Section 3306(u) of Title 26 of the United States Code) that employed one or more workers on or after December 21, 2000, and prior to the operative date of the statute adding this subdivision at the 2001 portion of the 2001–02 Regular Session of the Legislature that has not registered with the department by the operative date of the statute, shall register with the department within 15 days of that operative date. (2) The subject date for employers who register with the department under the provisions of paragraph (1) shall be December 21, 2000, or the date that employer first hired an employee, whichever is later.