The government has continued to pursue antitrust prosecutions since World War II. The Federal Trade Commission and the Antitrust Division of the Justice Department watch for potential monopolies or act to prevent mergers that threaten to reduce competition so severely that consumers could suffer. Four cases show the scope of these efforts:
In 1945, in a case involving the Aluminum Company of America, a federal appeals court considered how large a market share a firm could hold before it should be scrutinized for monopolistic practices. The court settled on 90 percent, noting "it is doubtful whether sixty or sixty-five percent would be enough, and certainly thirty-three percent is not."
In 1961, a number of companies in the electrical equipment industry were found guilty of fixing prices in restraint of competition. The companies agreed to pay extensive damages to consumers, and some corporate executives went to prison.
In 1963, the U.S. Supreme Court held that a combination of firms with large market shares could be presumed to be anti-competitive. The case involved Philadelphia National Bank. The court ruled that if a merger would cause a company to control an undue share of the market, and if there was no evidence the merger would not be harmful, then the merger could not take place.
In 1997, a federal court concluded that even though retailing is generally unconcentrated, certain retailers such as office supply "superstores" compete in distinct economic markets. In those markets, the merger of two substantial firms would be anti-competitive, the court said. The case involved a home office supply company, Staples, and a building supply company, Home Depot. The planned merger was dropped.
