205 ILCS 305/43
Without being required to take any action to perfect the same, a credit union shall have a lien on the shares, accumulated dividends or interest of a member in his individual, joint or trust account, for any sum due the credit union from said member or for any loan cosigned or guaranteed by him; provided, however, that a credit union shall not have a lien upon the funds in an Individual Retirement Account or an account established pursuant to Section 401(d) or (f) or Section 408(a) of the Internal Revenue Code or similar provisions of any future internal revenue law of the United States. A credit union may refuse to allow the withdrawal of a member's shares while the member has any outstanding obligation to the credit union. A member's shares may be offset against any sum due to the credit union. The enforcing of such lien shall be governed by this Act and by the terms of any written agreement between a credit union and its members and not by the provisions of any other statute.
205 ILCS 305/43