The referral systems operated by union organizations are required to observe several conditions:
1. All qualified workers reported to the referral system must be made available to the contractor without discrimination on the basis of union membership or other relationship to the union. The "closed shop" which limits referral to union members only is now illegal.
2. The contractor reserves the right to hire or refuse to hire any worker referred by the union on the basis of his or her qualifications.
3. The referral plan must be posted in public, including any priorities of referrals or required qualifications.