The City of Chicago (D) enacted a residential landlord and tenant ordinance establishing new landlord duties and tenant rights. Among other things, it required payment of interest on security deposits, allowed the tenant to withhold rent if the landlord violated the lease, allowed the tenant to make minor repairs and subtract the cost from the rent, and limited the amount that the landlord could charge the tenant for late rent. The purpose of this legislation was to promote public health, safety, welfare, and quality of housing. The Chicago Board of Realtors (P), a group of property owners, challenged the constitutionality of D's actions, arguing that D violated several clauses (the contracts clause, procedural and substantive due process, void for vagueness doctrine, equal protection, the takings clause, and the commerce clause). The district court denied the motion for preliminary injunction, stating that P did not have a reasonable likelihood of prevailing on the merits. P appealed, and the court of appeals affirmed the lower court's decision. P appealed.