Final answer:
The Robinson-Patman Act is the law that prohibited the charging of different prices that result in reduced competition, building on the foundation of the Clayton Antitrust Act which first addressed price discrimination.
Step-by-step explanation:
The law that prohibited charging buyers different prices if the result would reduce competition is the Robinson-Patman Act. This Act is an extension of the antitrust laws, aiming to prevent unfair competition and price discrimination. The Clayton Antitrust Act of 1914 was among the first to address price discrimination, while the Robinson-Patman Act of 1936 specifically targeted the practice of charging different prices to buyers if it harmed competition. Both pieces of legislation fall under the broader umbrella of antitrust laws, including the Sherman Antitrust Act and the Federal Trade Commission Act, which were enacted to protect trade and commerce against unlawful restraints and monopolies.