230 ILCS 5/15.4

The Board shall take disciplinary action authorized by subsection (d) of Section 9 of this Act or impose a civil penalty authorized by subsection (1) of Section 9 of this Act against any licensee which requires, as a condition precedent to employment, membership in any labor organization or association. Nothing in this Section shall prohibit an agreement between a labor organization or association and any such licensee which requires that, once employed, an employee be a member of the labor organization or association.