Competition Law
Competition law, or antitrust law as it is known in the United States, is designed to maintain free, competitive trade between companies. It prohibits the existence or restrains the activities of monopolies, cartels and anti-competitive behaviour. Mergers and acquisitions are subject to competition laws.
See also: http://ec.europa.eu/competition/, http://www.ftc.gov/bc/antitrust/index.shtm