15 U.S.C. §§13, 13a, 13b and 21a, United States antitrust law. In particular §§13 and 13a amended the Clayton Act that forbids any person or firm engaged in interstate commerce to discriminate in price to different purchasers of the same commodity when the effect would be to lessen competition or to create a monopoly. The statute is primarily designed to protect small shops from the buying power of big chains.