Section 35 ILCS 5/1406 - Identifying Numbers(a) Supplying of identifying numbers. When required by regulations prescribed by the Department: (1) Inclusion in returns. Any person required under this Act to make a return, statement, or other document shall include in such return, statement, or other document such identifying number as may be prescribed for securing proper identification of such person.(2) Furnishing number to other persons. Any person with respect to whom a return, statement, or other document is required under this Act to be made by another person shall furnish to such other person such identifying number as may be prescribed for securing his proper identification.(3) Furnishing number of another person. Any person required under this Act to make a return, statement, or other document with respect to another person shall request from such other person, and shall include in any such return, statement, or other document, such identifying number as may be prescribed for securing proper identification of such other person.(b) Limitation. (1) Except as provided in paragraph (2), a return of any person with respect to his liability for tax, or any statement or other document in support thereof, shall not be considered for purposes of paragraphs (2) and (3) of subsection (a) as a return, statement, or other document with respect to another person.(2) For purposes of paragraphs (2) and (3) of subsection (a), a return of an estate or trust with respect to its liability for tax, and any statement or other document in support thereof, shall be considered as a return, statement, or other document with respect to each beneficiary of such estate or trust.(c) Requirement of information. For purposes of this section, the Department is authorized to require such information as may be necessary to assign an identifying number to any person.