Antitrust laws are designed to maintain a competitive market environment by limiting practices that increase a firm's market power. This is done to prevent monopolies from forming and to ensure that all companies have a fair chance to compete in the marketplace. One way this is achieved is by making charging a price above marginal cost illegal. Marginal cost is the cost of producing one additional unit of a product, and charging a price above this cost can allow a company to gain an unfair advantage over its competitors. By enforcing antitrust laws and prohibiting such practices, the government can ensure that the marketplace remains fair and competitive for all businesses.