· 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, 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.