conspiracy, in law, agreement of two or more persons to commit a criminal or otherwise unlawful act. At common law, the crime of conspiracy was committed with the making of the agreement, but present-day statutes require an overt step by a conspirator to further the conspiracy. It is not necessary for guilt that the act be fully consummated. Many acts that would not be criminal if accomplished by an individual alone may nevertheless be the object of a conspiracy. With the rise of the labor movement in the 19th cent., British and American courts used this legal consent against unions; courts held that while an individual employee might lawfully abstain from work, the concerted stoppage of a group of employees, as in a strike, might be criminal. In 1875, Britain passed a law exempting unions from prosecution for conspiracy, and in 1932 the U.S. Congress passed a law that limited the power of federal courts to restrain union activity. Other controversial aspects of conspiracy laws include the modification of the rules of evidence and the potential for a dragnet. A statement of a conspirator in furtherance of the conspiracy is admissible against all conspirators, even if the statement includes damaging references to another conspirator, and often even if it violates the rules against hearsay evidence. The conspiracy can be proved by circumstantial evidence. Any conspirator is guilty of any substantive crime committed by any other conspirator in furtherance of the enterprise. It is a federal crime to conspire to commit any activity prohibited by federal statute, whether or not Congress imposed criminal sanctions on the activity itself. An individual injured by a conspiracy may sue the conspirators to recover damages.