Conspiracy, a difficult legal term to define, implies an agreement between 2 or more persons to commit an unlawful or criminal act, or an act which though lawful in itself becomes unlawful when done by the joint action of the agreeing parties, or for the purpose of using some unlawful means to commit what would otherwise be a lawful act, such as the breaking of a contract. Criminal conspiracy is condemned by the Canadian Criminal Code (s423) but sentences vary according to the intended crime.

For example, a conspiracy to commit murder is punishable by 14 years' imprisonment, while a conspiracy to prosecute an innocent person is punishable by 5 to 10 years' imprisonment. A conspiracy to have a woman commit adultery or fornication is punishable by 2 years; the conspirators may also be guilty, in this case, of ABDUCTION. Any conspiracy to achieve an unlawful purpose or a lawful purpose by unlawful means, eg, the use of bribes, is criminal and punishable by 2 years' imprisonment.

A mere intention to conspire or to commit an unlawful act is not sufficient to create criminal liability; there must be an actual agreement to act. The Criminal Code (s424) expressly provides that a conspiracy in restraint of trade (preventing another from carrying on his trade in a particular way or in a particular area) is not criminal when done by or on behalf of a trade union, which is therefore able to call its members out on strike regardless of any contract of service by which they may be bound, or is able to declare a sympathy strike on behalf of others engaged in a lawful strike.