Broker A's aggressive business model has caused other brokers to refuse to show listings. This action violates which law?

The correct answer is rooted in the application of antitrust laws, specifically the Sherman Antitrust Act. This federal law was established to promote fair competition in the marketplace and to prevent monopolistic practices. If Broker A's aggressive business model leads to other brokers avoiding showing listings, it suggests a form of collusion or coordinated behavior that restricts competition — essentially a boycott against Broker A’s listings. This behavior aligns with violations of the Sherman Antitrust Act, which prohibits actions that restrain trade or commerce among states.

The other options pertain to different areas of law. Regulation Z deals with the Truth in Lending Act and governs the disclosure of credit terms; the Real Estate Boycott Act specifically addresses acts of discrimination in housing, but is not as broadly applicable as the Sherman Act; and the Real Estate Settlement Procedures Act primarily focuses on regulating the practices of real estate settlement services to protect consumers from abuse and ensure transparency. Thus, they do not relate directly to the anticompetitive behavior described in the question.