The Sherman Antitrust Act, enacted in 1890 provides that: §1 Every K, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several States, or with foreign nations, is hereby declared to be illegal §2 Every person who shall monopolize, or attempt to monopolize, or combine or conspire with any other person or persons, to monopolize any part of the trade or commerce among the several States, or with foreign nations, shall be deemed guilty of a misdemeanor
The Clayton Antitrust Act of 1914 prohibits price discrimination between purchasers if "such discrimination substantially lessens competition or tends to create a monopoly in any line of commerce; prohibits sales that are contingent upon exclusive dealing or tying agreements; prohibits mergers and acquisitions that may "substantially lessen competition" and prohibits any person from being a director of two or more competing corporations.
The Robinson-Patman Act of 1936 prohibits price discrimination.