Hart-Scott-Rodino Act

The Hart-Scott-Rodino Antitrust Improvements Act of 1976 (Public Law 94-435, known commonly as the HSR Act) is a set of amendments to the antitrust laws of the United States, principally the Clayton Antitrust Act. The HSR Act was signed into law by President Gerald R. Ford on September 30, 1976. The context in which the HSR Act is usually cited is , title II of the original law.
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Often used in risk arbitrage. Antitrust act administered by U.S. Department of Justice and the F.T.C. that requires an investor to file a form with the government before he acquires an economic interest in the lesser of $15 million or 15% in a specific security. The government has thirty days to respond to the filer.